Low levels of vitamin D could increase the risk of cardiovascular events like heart attack, heart failure or stroke by 62 per cent, suggests a new study from the US.
And the outlook could be even worse for those with high blood pressure and low blood levels of vitamin with a doubling of the risk, report researchers in the journal Circulation - the Journal of the American Heart Association.
"The possibility of a causal link between vitamin D deficiency and cardiovascular disease is supported by biological plausibility, the demonstration of a temporal association, and the finding of a dose response between 25-OH D deficiency and risk," wrote lead author Thomas Wang from Harvard Medical School.
"These data raise the possibility that treatment of vitamin D deficiency, via supplementation or lifestyle measures, could reduce cardiovascular risk."
Interest in vitamin D has been increasing in recent months with an increasing number of studies linking the vitamin to protection against osteoporosis and certain cancers. There is also evidence that a higher intake of vitamin D may be helpful in preventing and treating high blood pressure, fibromyalgia, diabetes mellitus, multiple sclerosis and rheumatoid arthritis.
The researchers used data from the 1739 participants in the Framingham Offspring Study (average age 59 years, 55 per cent women, all Caucasian). None of the subjects had any heart health problems at the start of the study and the researchers used blood samples to measure levels of the 'storage' form of the vitamin, 25-dihydroxyvitamin D (25(OH)D).
Wang and co-workers found that 28 per cent of subjects had blood levels of 25(OH)D lower than 15 nanograms per millilitre (ng/mL). Over 5.4 years of follow-up, 120 people developed a cardiovascular event, and people with the lower vitamin D levels were 62 per cent more likely to develop these events than people with 25(OH)D levels over 15 ng/mL.
Although levels above 30 ng/mL are considered optimal for bone metabolism, only 10 per cent of the participants had levels in this range.
People with low vitamin D levels and high blood pressure (hypertension), defined as having a systolic and diastolic blood pressure (BP) greater than 140 and 90 mmHg, were at an increased risk, were found to be at a 113 per cent increased risk than those with normal blood pressure and higher vitamin D levels.
"We found that people with low vitamin D levels had a higher rate of cardiovascular events over the five-year follow-up period," said Wang. "These results are intriguing and suggestive but need to be followed up with further study."
"Vitamin D receptors have a broad tissue distribution that includes vascular smooth muscle and endothelium, the inner lining of the body's vessels," he added. "Our data raise the possibility that treating vitamin D deficiency, via supplementation or lifestyle measures, could reduce cardiovascular risk.
"What hasn't been proven yet is that vitamin D deficiency actually causes increased risk of cardiovascular disease. This would require a large randomized trial to show whether correcting the vitamin D deficiency would result in a reduction in cardiovascular risk."
Calls for raising the recommended daily allowance (RDA) of the vitamin have been growing after reports that higher intakes could protect against osteoporosis and certain cancers. Consumer awareness of these health links is also increasing with some outlets reporting massive boosts in sales.
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. The former is produced in the skin on exposure to UVB radiation (290 to 320 nm). The latter is derived from plants and only enters the body via the diet, from consumption of foods such as oily fish, egg yolk and liver.
Recent studies have shown, however, that sunshine levels in some northern countries are so weak during the winter months that the body makes no vitamin D at all, leading some to estimate that over half of the population in such countries have insufficient or deficient levels of the vitamin.
Moreover, increased skin pigmentation also reduces the effect of UVB radiation meaning darker skinned people are more at risk.
"The findings [of the new study] may have potentially broad public health implications, given the high prevalence of vitamin D deficiency in developed countries, the contribution of lifestyle and geography to vitamin D status, and the ease, safety, and low cost of treating vitamin D deficiency," concluded the researchers.
Both D3 and D2 precursors are hydroxylated in the liver and kidneys to form 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body.
January 2008, doi:10.1161/CIRCULATIONAHA.107.706127
"Vitamin D Deficiency and Risk of Cardiovascular Disease"
Authors: T.J. Wang, M.J. Pencina, S.L. Booth, P.F. Jacques, E. Ingelsson, K. Lanier, E.J. Benjamin, R.B. D'Agostino, M. Wolf, R.S. Vasan