August 22, 2024, 7:12 pm | Read time: 6 minutes
Vitamin D promotes the absorption of calcium and thus the hardening of bones. It’s logical, then, that consumers hope for strong bones from supplements. But do they really help? What do they really do? FITBOOK editor Melanie Hoffmann has reviewed the studies.
Vitamin D is important for bone health. This fact has become common knowledge, leading more people to turn to supplements, especially during the darker months. This should result in fewer bone fractures and breaks among the general population, right? Researchers at Harvard’s Brigham and Women’s Hospital have explored this question in a large-scale study to determine what vitamin D supplements actually do for bones.
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Overview
Over 5 Years of Daily Vitamin D Pills
Harvard researchers recruited 25,871 men and women over 50 who were generally healthy. Tests showed, however, that some participants had low vitamin D levels at the start of the study. On average, participants had a blood vitamin D level of 30.7 nanomoles per liter, with levels below 30 defined as deficient. Participants were divided into two groups: one took 2,000 IU of vitamin D daily, about twice the daily requirement, and the other received a placebo. Five years later, scientists counted how many bone fractures occurred in each group. The results were published in 2022 in the New England Journal of Medicine.1
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Why a Vitamin D Supplement May Not Be Beneficial for Bones
Adherence to intake recommendations was 87.3 percent after two years and 85.4 percent after five years. After the follow-up period, it was found that the average vitamin D levels in the supplement group increased from 29.2 to 41.2 nanomoles per liter, while those in the placebo group slightly decreased from 30.0 to 29.4 nanomoles per liter.
Regarding bone health, the result was surprising. For most participants, it made no difference whether they took the placebo or the actual supplement. In numbers:
- Among those who received vitamin D, 769 out of 12,927 participants had fractures–that’s six percent
- And among those who received the placebo, 782 out of 12,944 had fractures–also six percent
Study leader Dr. Meryl LeBoff summarized in a university statement: “Vitamin D intake did not lead to a lower fracture risk than the placebo in generally healthy middle-aged adults.”2 In other words, vitamin D supplements can do little for the bones of healthy people.
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Helpful Only for People with Low Bone Density
The researcher admits that patients with lower bone density or osteoporosis can indeed benefit from a daily extra dose of vitamin D. “Most study participants did not have a deficiency and may have already reached the vitamin D level required for bone health.”
Risk Groups for Vitamin D Deficiency
The German Nutrition Society identifies risk groups for vitamin D deficiency as people who spend little or no time outdoors in the sun or only with their bodies completely covered. This includes particularly mobility-impaired, chronically ill, and elderly people in need of care. People with darker skin are also at higher risk for deficiency.
Therefore, before resorting to supplements on suspicion, it should always be medically clarified whether a deficiency exists.
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Study Assessment
The strengths of the study include the large and diverse sample and the high adherence to therapy among participants. Additionally, fractures that occurred during the study were carefully assessed and confirmed. The measurement of 25-hydroxyvitamin D levels was calibrated according to the standards of the U.S. Centers for Disease Control and Prevention.
However, the study also has weaknesses. A key point is that only one specific vitamin D dose was examined. Moreover, the study was not designed to test the effect of vitamin D supplementation in individuals with proven vitamin D deficiency. Only a small percentage of study participants (2.4 percent) had a vitamin D level of less than 12 nanomoles per liter, limiting the generalizability of the results to this group. Although a subgroup analysis was conducted, it did not yield significant results–likely due to the small number of participants.
Finally, the study authors noted that the results may not be applicable to certain groups, such as adults with osteoporosis or osteomalacia or older people in nursing homes.
Not Just for Bones–Other Uses for Vitamin D
Vitamin D is involved in numerous metabolic processes, so a deficiency is suspected not only to promote depression but also to make affected individuals more susceptible to infections. This also applies to deadly diseases like cancer. According to a study by the German Cancer Research Center (DKFZ) in Heidelberg, 30,000 cancer deaths could be prevented annually in Germany if the elderly population were adequately supplied with vitamin D (FITBOOK reported).3 Another study published in 2022 found that daily vitamin D supplements could reduce the rate of autoimmune diseases in those over 50 by 22 percent.4 But again, where there is no deficiency, there is no need.