Medical News Today recently reported on a study from the University of California-San Diego School of Medicine, which suggests a link between vitamin D deficiency and premature death. Now, new research published in the BMJ links vitamin D deficiency to increased risk of death from all causes - including cardiovascular disease and cancer - and it may even play a part in cancer prognosis.
The main source of vitamin D is from the sun, and some foods - such as fatty fish (tuna, mackerel), cheese and fortified cereals - contain the vitamin. Vitamin D supplements can also boost levels in the body.
Vitamin D deficiency can be caused by low exposure to sunlight, low consumption of dietary vitamin D over a period of time, problems with kidney or digestive tract function and obesity.
Low levels of the vitamin have been associated with numerous health problems, such as increased risk of death from cardiovascular disease (CVD), higher risk of cognitive impairment in later life, increased risk of asthma among children and cancer.
But the researchers of this latest study say that so far, it has been unclear how vitamin D production in the body influences death.
Findings 'remarkably consistent'
The team set out to determine whether there was an association between vitamin D deficiency and deaths from all-causes, CVD and cancer.
They analyzed data from eight population-based studies from Europe and the US involving 26,018 participants between the ages of 50 and 79. Subjects were followed for 16 years.
Researchers found an association between low vitamin D levels and all-cause mortality - including CVD and cancer.
During follow-up, 6,695 deaths occurred. Of these, 2,624 were from CVD and 2,227 were from cancer.
The team found a link between participants with the lowest vitamin D levels - as determined by 25-hydroxyvitamin D (25(OH)D) concentrations in blood - and death from CVD. This association was found in participants with and without a history of the disease.
The team also found an association between low vitamin D levels and death from cancer among participants with a history of the disease. However, no such association was found among participants without a history of cancer, the researchers say, which indicates that vitamin D may be important in cancer prognosis.
But the team points out that they "cannot exclude reverse causality, that is, that the cancer might have led to low 25(OH)D levels."
"Furthermore," they add, "our study with the endpoint cancer mortality cannot make assumptions about a potential role of vitamin D in early phases of the carcinogenic process."
The researchers note that the findings were consistent across difference study populations, sexes, age groups and the time of year when blood tests were conducted "even though 25(OH)D cut-off values varied."
Before vitamin D supplements can be recommended to those with vitamin D deficiency, the study authors say further research is warranted:
"Despite levels of 25(OH)D strongly varying with country, sex, and season, the association between 25(OH)D level and all-cause and cause-specific mortality was remarkably consistent.
Results from a long-term randomized controlled trial addressing longevity are being awaited before vitamin D supplementation can be recommended in most individuals with low 25(OH)D levels."
However, other studies have questioned the benefits of vitamin D supplementation. Earlier this year, Medical News Today reported on a study published in The Lancet Diabetes & Endocrinology, which suggests the supplements are unlikely to reduce the incidence of numerous health problems, including cancer.
More recent research, also published in the BMJ, added to the argument against the use of vitamin D supplements, suggesting there is "no clear evidence" of their health benefits.