New European research has found that individuals with low levels of vitamin D may have a higher risk of an early death, particularly if they have diabetes.
Carried out by researchers at the Medical University of Vienna, Austria, the new study looked at data gathered from 78,581 patients with an average age of 51 who had blood tests taken to measure the levels of 25-hydroxyvitamin D (25D), more commonly known as vitamin D.
A vitamin D level of 50 nmol/L, which is the commonly used cut-off value for vitamin D deficiency, was used in the study as a reference value for comparing other vitamin D levels. The researchers defined a high level of vitamin D at 90 nmol/L and a low level at 10 nmol/L.
The researchers then matched this data with the Austrian national register of deaths to see how many participants died in the follow-up period, which for some participants lasted for nearly 20 years.
The findings, presented at this year's Annual Meeting of the European Association for the Study of Diabetes (EASD) in Barcelona, Spain, showed that vitamin D levels of 10 nmol/L or less were associated with a 2 to 3-fold increase in risk of death. The association was particularly strong for patients aged 45 to 60 years, who had a 2.9 times increased risk.
In contrast, high levels of vitamin D, set at 90 nmol/L or greater, were associated with a 30 to 40 percent reduced risk in all-cause mortality. Once again, the effect was strongest among those who were 45 to 60 years of age, who showed a 40 percent reduction in risk.
However, the researchers failed to find a statistically significant association between vitamin D levels and mortality in patients over the age of 75.
When looking at specific causes of death, the strongest associations were not between vitamin D and cardiovascular disease or cancer, a finding which surprised the authors. Instead, vitamin D was strongly associated with a risk of death from diabetes, with participants in the vitamin D deficient group (less than or equal to 50 nmol/L) showing a 4.4 times higher risk of death from the disease than participants whose vitamin D was above 50 nmol/L.
The researchers also found no evidence that higher vitamin D levels above 100 nmol/L increased the risk of death, despite concerns that vitamin D at higher levels can have a negative effect.
"Our survival data from a large cohort, covering all age groups, from a population with minimal vitamin D supplementation at old age, confirm a strong association of vitamin D deficiency (under 50 nmol/L) with increased mortality. This association is most pronounced in the younger and middle-aged groups and for causes of deaths other than cancer and cardiovascular disease, especially diabetes," concluded the researchers, adding that, "Our findings strengthen the rationale for widespread vitamin D supplementation to prevent premature mortality, emphasize the need for it early in life and mitigate concerns about a possible negative effect at higher levels."