Too little vitamin D, or vitamin D deficiency, can have severe health consequences in both children and adults.
In children, severe vitamin D deficiency can result in rickets, a rare condition in which the bone tissue does not properly mineralize, leading to soft bones and skeletal deformities.
In adults, severe vitamin D deficiency can result in osteomalacia. Osteomalacia is a softening of the bones from a loss of bone mineral content. It includes both muscle weakness and bone pain.
Signs of vitamin D deficiency can include mood changes, bone loss, muscle cramps or weakness, bone and joint pain, depression, and fatigue. The older you get, the more likely you are to have vitamin D deficiency because as you age, it becomes harder for your body to naturally produce vitamin D.
The Study
The Harvard study, “Effect of High-Dose Vitamin D Supplementation on Volumetric Bone Density and Bone Strength A Randomized Clinical Trial,” was conducted over a three-year period by Lauren A. Burt, Ph.D.; Emma O. Billington, M.D., F.R.C.P.C.; Marianne S. Rose, Ph.D.; Duncan A. Raymond, M.S.; David A. Hanley, M.D., F.R.C.P.C.; and Steven K. Boyd, Ph.D.
The study included 311 community-dwelling healthy adults without osteoporosis, aged 55 to 70 years. Its objective was to assess whether higher-dose vitamin D supplementation improves bone mineral density and bone strength. The authors hypothesized that a higher dose of vitamin D has a positive effect on measures of bone mineral density and strength.
During the double-blind, randomized clinical trial, the adults were treated with vitamin D during that period and calcium intake was monitored. Those adults not consuming the recommended dietary allowance of calcium received calcium supplements. The adults were treated with vitamin D in dosages of 400 IU per day, 4,000 IU per day, or 10,000 IU per day.
The study found that “at a dose of 4,000 IU per day or 10,000 IU per day, compared with 400 IU per day, resulted in statistically significant lower radial bone mineral density; tibial bone mineral density was significantly lower only with the daily dose of 10,000 IU.” Further, “there were no significant differences in bone strength at either the radius or tibia.”
The results of the study were the opposite of what the researchers hypothesized. The researchers had hypothesized that an increase in vitamin D supplementation would result in an increase in bone strength and density. However, the results of the study were a negative dose-response. Higher doses of vitamin D supplementation were associated with significantly greater loss of bone.
The researchers cautioned that this result could only be confirmed with additional research. Thus, “the appropriate interpretation of this study is that for maintenance of bone quality in healthy vitamin D-sufficient adults, these results do not support a skeletal benefit of vitamin D doses well above the recommended dietary allowance.”
Criticism
Responses to the Harvard study have not all been positive. At the beginning of 2020 doctors in Chongqing, China commented on the study. Their criticism was regarding the authors’ conclusion that “among healthy adults, supplementation with higher doses of vitamin D did not result in improved bone health.” The doctors said that this statement “could be misleading.”
Their reasoning looked to the patients’ medical histories and their relationship to vitamin D deficiency. The doctors said that the study population did not include healthy adults because the patients had medical histories that included “cancer, cardiovascular-related disease, type 2 diabetes, and rheumatoid arthritis.” These diseases may relate to vitamin D deficiency and therefore “such patients should have been excluded.”
How Much Vitamin D Is Safe?
It is clear that some vitamin D is necessary for your health; however more research is needed to determine whether higher doses may be harmful. In the meantime, how much vitamin D should be taken by an individual is a determination that should be made by each individual and his or her doctor.
