Alpha-methylselenobutanoic acid

Other Names

No alternative names.

Synopsis

Alpha-Methylselenobutanoic Acid (2-Hydroxy-4-Methylselenobutanoic Acid; HMSeBA)

1. Identity, Nomenclature, and Chemical Characterization

The compound commonly described in the scientific and regulatory literature under the informal descriptor alpha-methylselenobutanoic acid corresponds to the systematic chemical entity 2-hydroxy-4-(methylseleno)butanoic acid, universally abbreviated as HMSeBA. It is also widely referred to by the trade-associated name hydroxy-selenomethionine (OH-SeMet) and, in authorized regulatory designations, as the hydroxy-analogue of selenomethionine. HMSeBA is synthetic R,S-2-hydroxy-4-methylselenobutanoic acid, known as the hydroxy-analog of selenomethionine (SeMet), in which the second carbon amino group is substituted by a hydroxyl group.

Structurally, HMSeBA is a four-carbon (butanoic acid) chain bearing a methylseleno (–Se–CH₃) group at the 4-position (the γ-carbon or "methio-" carbon, analogous to the side chain of methionine) and a hydroxyl group at the 2-position (the α-carbon) in place of the amino group found in selenomethionine. This makes it a direct structural analogue of the sulfur-containing compound DL-2-hydroxy-4-(methylthio)butanoic acid (HMTBA, or methionine hydroxy analogue), with selenium substituted for sulfur at the thioether position. The additive hydroxy-analogue of selenomethionine consists of synthetic R,S-2-hydroxy-4-methylselenobutanoic acid (HMSeBA) and is intended to be used as a source of the essential trace element selenium for all animal species/categories.

HMSeBA exists as a racemic mixture (R,S) at the 2-position chiral centre. The compound has a selenium content of 2%, which is much higher than other organic selenium sources. This relatively high elemental selenium mass fraction (approximately 2% w/w Se) is a practical advantage in feed and supplement formulation compared with selenomethionine-based yeast products.

It is important to distinguish HMSeBA from two related but distinct research compounds that share partial nomenclature. First, Se-methylselenocysteine (MeSeCys) is a naturally occurring organoselenium amino acid found in Allium and Brassica species. Methylselenocysteine is found in many vegetables: "as much as 80% of the total selenium" found in Allium species (onion, leek, garlic, ramps), Brassica species (broccoli, radish, Brussels sprouts, cabbage), and milk vetch (Astragalus species, Fabaceae) is present as Se-methylselenocysteine. Second, alpha-methylselenocysteine ((αMe)Sec) is a fully synthetic, unnatural amino acid engineered as a laboratory tool. It is a derivative of selenocysteine (Sec) described as a useful chemical tool to study selenoenzyme mechanisms; (αMe)Sec is identical to Sec except the Cα-H is replaced with a Cα-methyl group, which prevents this derivative from undergoing oxygen-mediated β-syn elimination to dehydroalanine, a common problem with Sec-containing peptides and proteins. Neither of these compounds is identical to HMSeBA, and published research on each should not be conflated.

2. Natural Sources and Occurrence

HMSeBA as a discrete chemical entity is not found as a significant endogenous constituent of common plant or animal foods. It is instead a fully synthetic compound produced by chemical synthesis. A pure chemically synthesized form of SeMet, such as hydroxy-selenomethionine (OH-SeMet, also known as 2-hydroxy-4-methylselenobutanoic acid — HMSeBA), has been authorized as feed additive, providing more than 98% of total selenium in the form of SeMet.

Its structural precursor in the metabolic sense, selenomethionine, is the principal organic selenium form found in nature, and selenium-rich foods are its ultimate dietary source. Garlic and onion, broccoli, and wild leek have the ability to accumulate selenium from soil; these Se-enriched plants present a greater protection against carcinogenesis than common plants, and two Se-compounds possessing anti-cancer activity have been identified: Se-methylselenocysteine and γ-glutamyl-Se-methylselenocysteine. In garlic, Se-methionine and Se-methylselenocysteine were identified by LC–ICP–MS; γ-glutamyl-Se-methylselenocysteine was shown to be the most abundant form of Se in the garlic. These natural plant organoselenium compounds are metabolic relatives of HMSeBA but are not the same compound.

The selenium content of food crops, and therefore the availability of organoselenium metabolites as precursors for synthetic HMSeBA, is strongly soil-dependent. The amount of selenium in soil can affect the selenium content of foods. Selenium deficiency is very rare in the United States and Canada. In regions of low soil selenium, biofortification approaches using HMSeBA as a feed additive have been studied as a strategy to increase the selenium content of food animal products for human consumption.

3. Common Forms and Preparations

HMSeBA is commercially available primarily as a liquid or solid feed additive formulation. One commercial product named Selisseo® (SO) has been developed; selenium in this product is present as 2-hydroxy-4-methylselenobutyric acid (HMSeBA). The compound is manufactured and distributed mainly by Adisseo France SAS. The 2-hydroxy-4-methylselenobutanoic acid (HMSeBA, Selisseo® 2% Se) has been supplied by Adisseo France S.A.S.

Forms of selenium that are commonly found in dietary supplements include selenomethionine, selenium-enriched yeast, sodium selenite, and sodium selenate. HMSeBA has a distinct regulatory status from these classical forms: its primary authorized use, at the time of the published literature reviewed here, is as an animal feed additive rather than as a direct human dietary supplement. Hydroxy-selenomethionine (HMSeBA) is a novel selenium source that first entered the market in 2013, and it received approval as a source of selenium in beef and dairy cattle feed in the US in 2021.

In animal nutrition studies, HMSeBA is typically incorporated into complete compound feeds (pelleted or mash diets), administered at controlled selenium doses expressed as milligrams of elemental selenium per kilogram of feed dry matter (mg Se/kg DM). Human-targeted supplement preparations containing HMSeBA as the named active ingredient are not the subject of the peer-reviewed clinical evidence base reviewed here; all clinical and mechanistic studies identified involve animal (livestock) models.

4. Traditional and Historical Use

HMSeBA is an entirely synthetic compound first introduced commercially in 2013. It has no documented history of traditional use in any ethnomedical, herbal, or food culture, as it does not exist in nature in appreciable amounts and could not have been used prior to its synthesis and commercial development.

The broader context of selenium as a nutritional concern does have a modern scientific history rooted in the mid-twentieth century. Scientists demonstrated that selenium was incorporated into the chemical structure of the enzyme glutathione peroxidase, an enzyme necessary to protect erythrocyte cell membranes and other biological structures against toxic reactions with highly reactive oxygen-derived species such as peroxides and superoxides; the role of selenium in the biochemistry of glutathione peroxidase has been studied in some detail, and the most current medical information confirms that trace amounts of selenium are required to maintain normal human health.

Traditional use of selenium-hyperaccumulating plants (such as Astragalus species, known as locoweed) was documented in livestock poisoning contexts, and the recognition of selenium as an essential rather than purely toxic element emerged progressively in the latter half of the twentieth century. The use of selenium as a diet supplement for humans and animals, although recent, is also well known. HMSeBA itself emerged from this modern nutritional science context rather than from any traditional botanical practice.

5. Key Active Constituents and Established Mechanisms of Action

5.1 Post-Absorptive Conversion to Selenomethionine

The primary mechanism by which HMSeBA exerts its biological effects is through its metabolic conversion, following absorption, into selenomethionine (SeMet). After being absorbed, HMSeBA is metabolised to selenomethionine; consequently, no residues of the compound itself occur in animal tissues and products. This conversion is analogous to the well-characterized conversion of the sulfur analogue (DL-HMTBA) to L-methionine via transamination and oxidoreduction reactions.

Little is known about the actual transport of HMSeBA across the gastrointestinal tract, but studies in poultry have demonstrated that the sulfur homolog of HMSeBA, DL-2-hydroxy-4-(methylthio)butanoic acid, is transported across the apical membrane by H⁺-dependent carrier-mediated mechanisms related to L-lactate transport; hydroxy-selenomethionine is a precursor of SeMet and is metabolized in the same way as SeMet. Seleno amino acid measurements conducted on different tissues of animals fed HMSeBA (SO) at 0.5 mg/kg of feed showed that HMSeBA is fully converted into selenomethionine and selenocysteine.

5.2 Incorporation into Selenoproteins

Once converted to selenomethionine and selenocysteine, the selenium from HMSeBA enters the general selenoprotein biosynthesis pathway. Selenium is incorporated non-specifically into proteins in place of methionine (as SeMet) and specifically as selenocysteine into the active sites of dedicated selenoproteins. Selenium is a vital nutritional trace element involved in the composition of at least 25 selenoproteins that show catalytic or antioxidant capacities.

The selenoproteins of greatest functional importance include the glutathione peroxidase (GPX) family and the thioredoxin reductase (TXNRD) family, among others. Maternal HMSeBA supplementation significantly upregulated mRNA levels of selenoprotein S (SELS) in the jejunum of newborn and weaned piglets; additionally, HMSeBA treatment significantly increased the expression of glutathione peroxidase 4 (GPX4) and SELS, while decreasing ROS levels and the expression of endoplasmic reticulum (ER) stress markers induced by hydrogen peroxide in IPEC-J2 cells.

5.3 Antioxidant Defense Enhancement

HMSeBA's principal documented mechanism is the enhancement of enzymatic antioxidant defenses. The organic selenium source HMSeBA has been proved to decrease intestinal inflammation and autophagy by improving the expression of selenoproteins. Key antioxidant enzyme activities consistently reported to be elevated following HMSeBA supplementation include glutathione peroxidase (GPX), superoxide dismutase (SOD), thioredoxin reductase (TXNRD), total antioxidant capacity (T-AOC), and glutathione reductase (GR). Conversely, the lipid peroxidation marker malondialdehyde (MDA) is typically reduced.

As an organic selenium source, HMSeBA inhibits cell apoptosis by reducing lipid peroxidation and ROS production, thereby exerting a therapeutic antioxidant effect.

5.4 Regulation of Specific Selenoprotein Genes

HMSeBA supplementation has been shown to modulate the gene expression of multiple distinct selenoproteins beyond GPX4 and SELS, including selenoprotein P (SELENOP), selenoprotein W (SELENOW), selenoprotein O (SELENOO), and selenoprotein H (SELENOH), as well as components of the thioredoxin and glutathione systems. Dietary supplementation with HMSeBA improved the gilts' tissue selenium content (except in the thymus) and selenoprotein P (SelP1) concentration when compared to the sodium selenite or control group.

5.5 Tissue Distribution and Bioavailability Advantage

HMSeBA demonstrates superior selenium deposition in peripheral tissues, particularly skeletal muscle, compared with inorganic selenium sources (sodium selenite) and selenium yeast. Plasma, liver, and muscle Se concentrations were improved by all Se sources compared with the negative control group; between selenium sources, a significant dose effect was observed, and muscle Se concentrations were improved such that SO (HMSeBA) > SY (selenium yeast) > SS (sodium selenite); moreover, the relative muscle Se enrichment comparison, using linear regression slope ratio, indicated an average of 1.48-fold (95% CI 1.38, 1.58) higher Se deposition in muscle for SO compared with selenium yeast.

Compared with inorganic selenium sources, the use of HMSeBA in animal nutrition would result in a similar increase in selenium deposition in animal tissues/products as that resulting from selenised yeast.

5.6 Signaling Pathway Modulation

In studies examining mammary gland biology under heat stress, HMSeBA has been shown to act via the PI3K/AKT/mTOR signaling pathway. HMSeBA significantly regulated antioxidant capacity, inhibited inflammation, and regulated tight junction protein expression in the blood-milk barrier via PI3K/AKT/mTOR signaling pathway, so as to alleviate mammary gland damage and ensure its structure and function integrity. These findings are derived from cell and rodent models, and their applicability to human biology requires further investigation.

6. Scientific Evidence by Area of Application

Important note on the evidence base: The entirety of the identified peer-reviewed evidence for HMSeBA's biological effects is derived from animal models — principally swine (gilts, sows, piglets), poultry (broiler and laying hens), and dairy cattle (cows and heifers), with some in vitro cell work. No human clinical trials of HMSeBA as a direct dietary supplement have been identified in the peer-reviewed literature. All the following sections describe animal and in vitro evidence only, and the evidence strength for human applications must therefore be characterized as preliminary and indirect.

6.1 Antioxidant Status

Evidence level: Animal (multiple controlled trials) and in vitro; no human RCTs.

The most extensively documented effect of HMSeBA across species is enhancement of systemic antioxidant status. Multiple controlled animal trials have evaluated this outcome.

In swine: From weaning to the 19th day after the second estrus, 36 gilts (Duroc × Landrace × Yorkshire) were assigned to three treatments: control group, sodium selenite group (0.3 mg Se/kg), and HMSeBA group (0.3 mg Se/kg HMSeBA). Dietary supplementation with HMSeBA improved the gilts' tissue selenium content (except in the thymus) and selenoprotein P (SelP1) concentration when compared to the sodium selenite or control group. Compared with the control group, the antioxidant enzyme activity in the tissues from gilts in the HMSeBA group was increased, and the concentration of malondialdehyde in the colon had a decreasing trend.

In dairy cattle: One study aimed to evaluate the effect of hydroxy-selenomethionine (HMSeBA) on milk performance, antioxidative status, and Se concentrations in the milk and plasma of mid-lactation dairy cows compared with sodium selenite (SS). Fifty mid-lactation dairy cows received the same basal diet containing 0.06 mg of Se/kg of DM and were assigned to a negative control (without Se supplementation), SS supplementation (0.3 mg of Se/kg of DM), or HMSeBA supplementation (0.1, 0.3, or 0.5 mg of Se/kg of DM); the experiment lasted for 10 weeks, including a pretrial period of 2 weeks. Results indicated that neither Se supplementation nor Se source affected dry matter intake, milk yield, milk composition, or blood biochemical parameters, except for milk fat percentage. The SO-0.3 group showed higher serum activity of glutathione peroxidase, total antioxidant capacity, and superoxide dismutase than the SS-0.3 group; furthermore, HMSeBA supplementation linearly increased the activities of serum glutathione peroxidase and superoxide dismutase, but decreased malondialdehyde content.

Under oxidative stress conditions (heat stress model): One study used heat stress as an oxidative stress model to examine the effects of hydroxy-selenomethionine (HMSeBA) on selenium bioavailability, antioxidant status, and performance when fed to dairy cows. Eight mid-lactation Holstein dairy cows (141 ± 27 days in milk, 35.3 ± 2.8 kg of milk/day, parity 2 or 3) were individually housed in environmental chambers and randomly assigned to 1 of 2 treatments: inorganic Se supplementation (sodium selenite; 0.3 mg of Se/kg of dry matter) or HMSeBA supplementation (0.3 mg of Se/kg of dry matter). The trial was divided into 3 continuous periods: a covariate period (9 days), a thermal neutral period (28 days), and a heat stress period (9 days). Supplementation with HMSeBA increased total antioxidant capacity and decreased malondialdehyde, hydrogen peroxide, and nitric oxide serum concentrations compared with sodium selenite-fed controls.

6.2 Selenium Tissue Enrichment and Bioavailability

Evidence level: Multiple controlled animal trials; no human bioavailability trials identified.

Across broiler, turkey, swine, and dairy cattle studies, HMSeBA consistently demonstrates superior tissue selenium deposition compared with inorganic sources and parity or superiority to selenized yeast. This is clinically and nutritionally relevant as a strategy for biofortification of animal-derived foods.

One study evaluated the effects of HMSeBA on selected performance criteria and selenium deposition in eggs of laying hens. Isa Brown laying hens, 18 weeks of age, were randomly allocated to two dietary treatments and fed for 10 weeks. The hens were fed corn-soybean meal-based diets comprising a control basal diet without Se supplementation and a test diet supplemented with Se at 0.2 mg/kg from HMSeBA. No difference was observed among dietary treatments on feed intake, egg weight, and laying rate, whereas egg yolk fatty acid profile and vitamin E content were positively influenced by HMSeBA supplementation. Hens fed the Se-supplemented diet exhibited greater egg yolk total Se contents, which averaged 21.2 mg/100 g dry matter compared to the control diet (11.7 mg/100 g DM).

One study determined the effects of supplementing pregnant heifers with HMSeBA during the last 8 weeks of pregnancy on dam and calf Se status. A total of 42 in-calf heifers were recruited and randomly allocated to 1 of 3 treatments (negative control, sodium selenite, or HMSeBA). Animals were blocked by body weight, body condition score, and expected calving date before treatment allocation; following enrollment, all animals underwent a 7-week wash-out period, after which they received their respective supplements, top-dressed daily onto a basal diet for the last 8 weeks of pregnancy.

The EFSA FEEDAP Panel, in assessing bioavailability, noted that based on the response of plasma glutathione peroxidase activity and the plasma/liver concentration of selenium in chickens for fattening and pigs for fattening, HMSeBA is an efficacious source of selenium for all animal species/categories.

6.3 Reproductive Performance and Follicular Development

Evidence level: Animal (swine); no human evidence.

One study evaluated the effects of dietary HMSeBA supplementation on follicle development in vivo and on the function of ovarian granulosa cells in vitro. Thirty-six gilts were randomly assigned to control diet, sodium selenite diet (0.3 mg Se/kg), or HMSeBA diet (0.3 mg Se/kg). HMSeBA and sodium selenite supplementation both increased the total selenium content in liver and serum compared with control, while HMSeBA increased the total selenium content in liver compared with the sodium selenite group. HMSeBA tended to increase the total selenium content in ovary compared with control.

In vitro, HMSeBA significantly increased cell proliferation of granulosa cells at 5 ng/ml. Estradiol secretion is an important manifestation of the physiological function of granular cells, and HMSeBA significantly increased the E2 (estradiol) concentration compared with the control treatment at 5 and 10 ng/ml.

HMSeBA supplementation during sow pregnancy increased the number of total born piglets, decreased piglet birth interval, improved concentrations of total selenium, and also improved activity of antioxidant enzymes compared with control and sodium selenite treatment.

6.4 Intestinal Health, Endoplasmic Reticulum Stress, and Gut Microbiota

Evidence level: Animal (swine) and in vitro; no human evidence.

Endoplasmic reticulum (ER) stress, which can be induced by reactive oxygen species (ROS) and multiple factors, is associated with numerous intestinal diseases. HMSeBA has been proved to decrease intestinal inflammation and autophagy by improving the expression of selenoproteins; however, it remained unclear whether HMSeBA could alleviate intestinal ER stress by decreasing excessive production of ROS products.

Maternal HMSeBA supplementation significantly upregulated mRNA levels of selenoprotein S (SELS) in the jejunum of newborn and weaned piglets compared with the control group, while decreasing the gene expression and protein abundance of ER stress markers in the jejunum of LPS-challenged weaned piglets. HMSeBA treatment significantly increased the expression of GPX4 and SELS, while decreasing ROS levels and the expression of ER stress markers induced by hydrogen peroxide in IPEC-J2 cells. Furthermore, knockdown of GPX4 did not enhance the ER stress signal induced by hydrogen peroxide, but the lack of GPX4 would cause further deterioration of ER stress signaling in the absence of SELS.

Regarding gut microbiota, HMSeBA supplementation in gilts was associated with changes in intestinal microbiota composition. The HMSeBA group increased the protein concentrations of IL-2 and IgG in serum. The immunological underpinning involves the documented role of selenium status in supporting mucosal immunity; low selenium content may affect intestinal mucosal immunity, and in commercial broilers, selenium deficiency reduced the content of soluble IgA in the duodenal mucosa and increased the level of pro-inflammatory cytokine IL-1β.

6.5 Immune Function

Evidence level: Animal (swine, poultry); no human evidence.

The immune system relies on a good selenium state to fight bacterial and viral infections, deal with oxidative damage, and regulate inflammation. Adding selenium in the basal diet of sows effectively increased the serum IgA, IgG, and IgM concentrations of sows and their offspring. HMSeBA-specific studies in gilts documented increases in serum immunoglobulin G (IgG) and interleukin-2 (IL-2) concentrations compared with controls.

6.6 Skeletal Muscle and Meat Quality (Livestock Applications)

Evidence level: Animal (swine); no human evidence.

Chronic heat stress (CHS) induces metabolic changes in skeletal muscle from growth to maintenance that jeopardize growth performance, carcass traits, and meat quality of pigs. One study investigated the protective effect of dietary organic selenium (hydroxy-4-methylselenobutanoic acid, OH-SeMet) on CHS-induced skeletal muscle damage in growing pigs, and the corresponding responses of selenoproteins. Forty (Landrace × Yorkshire) × Duroc pigs with an average live weight of 49.64 ± 2.48 kg were used in a 4-week trial and were randomly allotted to 5 groups: a control group raised on a basal diet in a thermoneutral environment (22 ± 2°C), and four CHS groups raised on a basal diet supplemented with Se 0.0, 0.2, 0.4, and 0.6 mg/kg as OH-SeMet, respectively, in a hyperthermal condition (33 ± 2°C).

6.7 Food Biofortification

Evidence level: Animal feeding trials; indirect relevance to human nutrition.

One application area with indirect human relevance is the use of HMSeBA to enrich animal-derived foods (eggs, muscle meat, milk) with selenium, thereby potentially improving selenium intake of consumers. Increasing doses of HMSeBA linearly increased the concentrations of total Se in the milk and plasma; HMSeBA improves antioxidant status and increases milk and plasma Se concentrations more effectively than sodium selenite, indicating that HMSeBA could replace sodium selenite as an effective organic Se source for lactating dairy cows. The broader selenium biofortification context is described by the NIH ODS as relevant to groups at risk of inadequate selenium intake, including people who eat diets that consist mostly of plant foods grown in local soils that are low in selenium.

7. Body Systems and Health Areas Associated with HMSeBA

Antioxidant / Redox Biology: Principal documented area; HMSeBA enhances GPX, SOD, TXNRD, and T-AOC while reducing MDA and ROS. All evidence is from animal models.
Gastrointestinal System: Documented reduction of intestinal ER stress, inflammation, and autophagy via upregulation of GPX4 and selenoprotein S in animal (piglet) and in vitro models.
Immune System: Documented increases in serum IgG and IL-2 in gilts; broader selenium-immunology links are well-established in the literature for selenium as an element.
Reproductive System: Evidence in swine for promotion of follicular development, granulosa cell proliferation and estradiol secretion, increased selenoprotein expression in the ovary, and improved reproductive outcomes in sows.
Skeletal Muscle: Evidence in swine that HMSeBA at doses of 0.2–0.6 mg Se/kg feed attenuates heat-stress-induced skeletal muscle damage and preserves selenoprotein expression.
Thyroid/Endocrine (indirect): HMSeBA, as a selenium source, supplies selenium for thyroid selenoproteins (including deiodinases); however, direct thyroid-specific studies with HMSeBA have not been identified in the reviewed literature. The NIH ODS notes that selenium deficiency can worsen iodine deficiency and increase the risk of thyroid disease: selenium deficiency can make iodine deficiency worse, increasing the risk of thyroid disease.
Mammary Gland / Lactation Biology: Evidence in dairy cattle models that HMSeBA alleviates heat-stress-induced blood-milk barrier disruption and reduces mammary gland inflammation via antioxidant and tight junction mechanisms.

8. Dosages Reported in Studies

All dosages below are as reported in published studies and refer to animal feed supplementation levels. No human clinical dosing data for HMSeBA have been identified in the peer-reviewed literature reviewed here.

Swine (gilts, sows, piglets): Thirty-six gilts were assigned to: control group, sodium selenite group (0.3 mg Se/kg), and HMSeBA group (0.3 mg Se/kg HMSeBA).
Broiler chickens (tissue enrichment): The first experiment compared Se sources at different concentrations (mg of Se/kg of feed): sodium selenite at 0.3; selenium yeast at 0.1 and 0.3; HMSeBA at 0.1 and 0.3; and a negative control (0), in broilers between 0 and 42 days of age.
Laying hens (egg biofortification): The test diet was supplemented with Se at 0.2 mg/kg from HMSeBA.
Growing pigs (heat stress/skeletal muscle): Four CHS groups were raised on a basal diet and supplemented with Se at 0.0, 0.2, 0.4, and 0.6 mg/kg as OH-SeMet, respectively.
Dairy cows (antioxidant status, milk Se): Dairy cows were assigned to sodium selenite supplementation (0.3 mg of Se/kg of DM; SS-0.3) or HMSeBA supplementation (0.1, 0.3, or 0.5 mg of Se/kg of DM).
Dairy cows (heat stress model): Eight mid-lactation Holstein dairy cows were randomly assigned to inorganic Se supplementation (sodium selenite; 0.3 mg of Se/kg of dry matter) or HMSeBA supplementation (0.3 mg of Se/kg of dry matter).
Pregnant heifers: One study investigated the effects of supplementing pregnant heifers with HMSeBA during the last 8 weeks of pregnancy; following a 7-week wash-out period, animals received their respective supplements top-dressed daily onto a basal diet.

The regulatory maximum for selenium supplementation from HMSeBA in animal feed was set by the EFSA FEEDAP Panel: to ensure consumer safety from consumption of food originating from animals supplemented with HMSeBA, the FEEDAP Panel concluded that selenium supplementation from the additive should not exceed a maximum of 0.2 mg Se/kg complete feed.

For human selenium intake as a nutrient more broadly, the NIH ODS notes that the doses of selenium in multivitamin/mineral supplements vary, but many contain 55 mcg. The tolerable upper intake level for selenium in humans, as established by authoritative bodies, applies to all forms of selenium (including organic forms). Early indicators of excess intake are a garlic odor in the breath and a metallic taste in the mouth. The most common clinical signs of chronically high selenium intakes, or selenosis, are hair loss and nail brittleness or loss. Other signs and symptoms include skin rash, nausea, diarrhea, fatigue, irritability, and nervous system abnormalities.

9. Safety Considerations and Relevant Interactions

9.1 Safety Evaluation in Animals (EFSA 2013)

The additive hydroxy-analogue of selenomethionine consists of synthetic R,S-2-hydroxy-4-methylselenobutanoic acid (HMSeBA) and is intended to be used as a source of the essential trace element selenium for all animal species/categories. Based on data from tolerance studies in chickens and turkeys for fattening and piglets, the additive is considered as safe for all species/categories up to the maximum authorised total selenium level in complete feed. After being absorbed, HMSeBA is metabolised to selenomethionine; consequently, no residues of the compound itself occur in animal tissues and products.

9.2 Occupational / Handler Safety

The additive should be regarded as an eye irritant, but should not be classified as a skin irritant or skin sensitiser. Inhalation exposure poses a hazard to users; the FEEDAP Panel concludes, therefore, that the formulation and conditions of use of the solid form of the additive should minimise user exposure by inhalation.

9.3 Environmental Safety

The use of HMSeBA in feed does not pose an additional risk to the environment, compared to other sources of selenium for which it will substitute, as long as the maximum authorised content in feedingstuffs is not exceeded.

9.4 Upper Limit and Consumer Safety (Food Chain)

The FEEDAP Panel has previously concluded that the selenium supplementation of feed by selenised yeast, by HMSeBA, by L-SeMet, or by DL-SeMet should be limited to a maximum of 0.2 mg Se/kg feed. This limit is set to protect consumers of animal-derived products (meat, eggs, milk) from excessive selenium intake through the food chain, recognizing that selenium from organic sources is deposited more efficiently in animal tissues than inorganic selenium.

9.5 Selenium Toxicity — General Principles

Because HMSeBA is entirely converted to selenomethionine after absorption, its toxicity profile is that of organic selenium species in general. Acute selenium toxicity has resulted from the ingestion of misformulated over-the-counter products that contain very large amounts of selenium; in 2008, for example, 201 people experienced severe adverse reactions from taking a liquid dietary supplement that contained 200 times the labeled amount of selenium.

Many studies have shown that organic selenium (methionine selenium, selenium yeast, selenium-enriched probiotics, etc.) has less toxicity and higher biological potency than inorganic selenium (sodium selenite and sodium selenate, etc.).

In an experiment, excessive dietary doses of 5 mg of Se/kg of feed from sodium selenite and HMSeBA showed a lower deleterious effect of HMSeBA on body weight and feed intake in comparison with standard selenium doses. This finding, from a broiler chicken study, suggests HMSeBA may have a marginally wider safety margin than inorganic selenium at supratherapeutic doses, consistent with organic selenium's general lower acute toxicity compared with inorganic forms.

9.6 Absence of Human Clinical Data

No human clinical safety data for HMSeBA as a directly administered dietary supplement have been identified in the peer-reviewed literature reviewed here. The safety conclusions documented above derive exclusively from animal (livestock) tolerance studies evaluated in the regulatory context of animal feed additives. Extrapolation of these safety findings to direct human consumption of HMSeBA as a dietary supplement ingredient requires dedicated human studies that, as of the literature reviewed, have not been published.

10. Regulatory Status

Hydroxy-selenomethionine (HMSeBA) is a novel selenium source that first entered the market in 2013, and it received approval as a source of selenium in beef and dairy cattle feed in the US in 2021. In the European Union, the EFSA FEEDAP Panel issued its scientific opinion authorizing HMSeBA as a nutritional feed additive for all animal species/categories in 2013, subject to the constraint that total selenium supplementation from the additive not exceed 0.2 mg Se/kg complete feed. The suggested citation for this regulatory opinion is: EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP); Scientific Opinion on safety and efficacy of hydroxy-analogue of selenomethionine as feed additive for all species. EFSA Journal 2013;11(1):3046.

11. Evidence Summary and Research Gaps

The available body of research on HMSeBA is substantial for an animal feed additive, encompassing controlled trials in multiple livestock species, mechanistic in vitro studies, and formal regulatory safety evaluation. However, the evidence base has several critical limitations when evaluated in the context of human supplementation:

All efficacy data are from animal models (swine, poultry, dairy cattle), with no published human clinical trials.
Bioavailability, optimal dosing, and long-term safety data for direct human consumption of HMSeBA have not been established.
Mechanistic studies involving cell signaling (PI3K/AKT/mTOR) and selenoprotein gene regulation are informative but conducted in rodent or in vitro systems.
The food-chain biofortification use (enriching eggs, milk, and meat with selenium through HMSeBA-fed animals) provides an indirect but plausible pathway through which HMSeBA research has human health relevance, though this is distinct from direct supplementation.
Apart from traditional selenium formulations, a new generation of selenium-based ingredients for dietary supplements is emerging; such next-generation ingredients, represented mainly by zerovalent selenium nanoparticles or selenized polysaccharides, slowly release bioactive selenium species and have lower toxicity, more controlled and/or targeted mechanisms of action, and fewer side effects. HMSeBA occupies a position between the classical forms and these emerging next-generation forms.

References

Health Conditions

Health conditions that Alpha-methylselenobutanoic acid may help support.

No conditions available.

Body Systems

Body systems that Alpha-methylselenobutanoic acid may help support.

No body systems available.