Low vitamin D levels alone do not cause osteoporotic fractures, according to a new study published in the American Association for Clinical Chemistry (AACC)'s Clinical Chemistry journal. These findings could resolve the ongoing debate over whether vitamin D supplements prevent these types of fractures and suggest that the general population should not rely on vitamin D by itself for this purpose, according to the study authors. 

Although vitamin D helps the body absorb minerals essential for bone health, previous studies have found conflicting evidence on whether low vitamin D levels actually increase the risk of osteoporotic fractures and whether vitamin D supplements can reduce the risk.

There has been a mixture of guidance over the years in recommendations for vitamin D supplements, according to the study authors. This led researchers from the Copenhagen University Hospital in Denmark to perform a large-scale analysis of low vitamin D levels and osteoporotic fractures. 

Using Mendalian randomization, the team identified 35,833 individuals who underwent genetic and vitamin D testing between the ages of 20 and 100 years as part of the decades-long Copenhagen City Heart and Copenhagen General Population Studies. The researchers were able to determine the number of genes each participant had that lowered their vitamin D levels. Following this, the team looked at the participants’ medical records to determine how many of them experienced osteoporotic fractures from 1981 to 2017.

A statistical analysis showed that the individuals with low blood levels of vitamin D had an increased risk for osteoporotic fractures compared with individuals with ≥50 nmol/L of vitamin D. Individuals with high numbers of vitamin D-lowering genes did not have a higher risk of osteoporotic fractures than those with fewer of these genes, according to the study authors.

The 2 results indicate that low vitamin D does not actually cause osteoporotic fractures and could be associated with fractures due to its sign as an overall unhealthy lifestyle.

"Our study is the first large scale study addressing whether vitamin D is causally related to fractures in the general population using genetics—that is, using nature's own randomized trial free of confounding," said Borge G. Nordestgaard, MD, one of the study authors in a press release. "[It suggests] that vitamin D per se is unlikely to be causally related to fractures. Summing the evidence from previous randomized trials with our new evidence thus suggests that benefit from vitamin D supplementation is likely to prevent osteoporotic fractures only if taken together with calcium."

Novel Research in AACC’s Clinical Chemistry Journal Shows That Vitamin D Supplements Do Not Prevent Osteoporotic Fractures. AACC. https://www.aacc.org/media/press-release-archive/2020/04-apr/research-in-clinical-chemistry-shows-that-vitamin-d-does-not-prevent-osteoporotic-fractures. Published April 7, 2020. Accessed April 14, 2020.