Rehmannia (Rehmannia glutinosa) is primarily used in Traditional Chinese Medicine (TCM), where it is considered a key herb for nourishing the "kidney" system. In TCM theory, the kidneys are seen as the root of vitality and are closely linked with bone health and the skeletal system. As such, Rehmannia is often incorporated into herbal formulas intended to support healthy bones, treat conditions like osteoporosis, and address symptoms that TCM attributes to "kidney deficiency," such as weak bones, lower back pain, and joint problems.

However, scientific research directly examining Rehmannia’s effect on bone health is limited. Some animal studies suggest that Rehmannia extracts may have beneficial effects on bone metabolism, possibly by influencing bone density and markers of bone turnover, but this evidence is preliminary and not yet confirmed in human clinical trials. No robust, large-scale human studies have validated its efficacy for improving skeletal health. Therefore, while its use is well-supported by traditional practice, scientific validation remains modest at best.

In summary, Rehmannia's reputation as a bone-supportive herb is grounded in traditional use and theory rather than in strong scientific evidence.