Low Vitamin D Linked to High Mortality

Vitamin D deficiencies are causally associated with increased mortality rates, according to a study published in BMJ.

Researchers from the University in Copenhagen in Denmark aimed to determine whether genetically low 25-hydroxyvitamin D levels are linked to increased mortality rates. The investigators defined low vitamin D as 20 nmol/L below the recommended 50 nmol/L minimum level in Denmark.

The researchers examined a total of nearly 96,000 white Danes from large-scale population studies who had genetic variants in DHCR7 and CYP2R1, which are known to affect vitamin D levels. The researchers followed the patients through 2013, during which time 10,349 had died.

The results of the study linked low vitamin D levels to increased all-cause mortality, cancer mortality, and other mortality, but not cardiovascular mortality. The findings aligned with the current literature, which generally concludes that low vitamin D levels may be causally linked to various mortalities. However, the present study authors pointed out that the link to cardiovascular mortality in previous literature might be due to unmeasured confounding factors.

“The clinical implication of our findings remain limited, as widespread vitamin D supplementation can be recommended only after benefit is shown in randomized intervention trials,” the authors concluded.

The investigators noted that more research is necessary, though many trials tracking vitamin D supplementation are set to start reporting results in 2017.

“Genes associated with low vitamin D levels involve an increased mortality rate of 30 percent and, more specifically, a 40 percent higher risk of cancer-related deaths,” said lead study author Shoaib Afzal, MD, PhD, in a press release. “An important factor in our study is that we have established a causal relationship.”

According to the authors, the average Dane obtains one-fifth of the recommended minimum vitamin D levels through diet, while the remainder comes from exposure to sunshine. Thus, supplements are important sources of vitamin D throughout the winter months in countries with reduced sunlight exposure, the researchers noted.