Researchers in Austria and Germany found that people who have low levels of vitamin D are more likely to have a shorter life span than people who do not. Further trials would be needed to find out if insufficient vitamin D actually causes early death, said the researchers, since their study was not designed to establish cause, but they were cautiously optimistic about a causal link.
The study is published in the 23 June online issue of the Archives of Internal Medicine and is the work of lead author Dr Harald Dobnig of the University of Graz in Austria and colleagues.
Dobnig and colleagues followed 3,258 male and female patients with an average age of 62 for nearly 8 years. The patients had been been referred for a heart examination (coronary angiography) between 1997 and 2000.
The researchers analysed levels of two types of vitamin D (25-hydroxyvitamin D and 1,25-dihydroxyvitamin D) in blood samples taken at enrollment (baseline) versus deaths due to cardiovascular and all causes.
The results showed that:
- 737 patients (22.6 per cent) died, including 463 deaths from cardiovascular causes during a median follow up of 7.7 years.
- Patients whose baseline 25-hydroxyvitamin D levels were below the mid-point of the group (the lower 2 quartiles) were at significantly higher risk of death from both cardiovascular and all causes.
- The effect stayed the same when the researchers eliminated cardiovascular risk factors in patients with different levels of physical activity, other illnesses, or coronary artery disease.
- The figures for 1,25-dihydroxyvitamin D showed similar but slightly weaker effects.
- Low levels of 25-hydroxyvitamin D also correlated significantly with blood level indicators of inflammation such as C reactive protein, and oxidative oxidative damage to cells.
Dobnig and colleagues concluded that:
“Low 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D levels are independently associated with all-cause and cardiovascular mortality. A causal relationship has yet to be proved by intervention trials using vitamin D.”
However, they cautiously suggested that while this study did not prove a causal link, together with evidence from other studies it is possible that vitamin D reduces the risk of atherosclerosis [narrowing of the arteries] and other cardiovascular problems.
They suggested that:
“Based on the findings of this study, a serum 25-hydroxyvitamin D level of 20 nanograms per milliliter or higher may be advised for maintaining general health.”
The journal editors also suggested that while this did not prove that the low levels of vitamin D caused the higher mortality risk, it appeared to be “biologically plausible and fit into the enlarging picture of adverse effects that may evolve with suboptimal vitamin D status”.
The researchers wrote in their background information that recent estimates suggested that 50 to 60 per cent of older people all over the world do not have enough vitamin D in their bodies, and the situation for younger people is not very different.
Previous research has shown that a low level of vitamin D is linked with falls, fractures, cancer, immune system problems, cardiovascular disease and high blood pressure. These effects are thought to be due to 1,25-dihydroxyvitamin D, which is made in the body and also converted from 25-hydroxyvitamin D.
Earlier this month, investigators from the Dana-Farber and the Harvard School of Public Health reported that higher levels of vitamin D were linked to lower risk of death from colon cancer.
“Independent Association of Low Serum 25-Hydroxyvitamin D and 1,25-Dihydroxyvitamin D Levels With All-Cause and Cardiovascular Mortality.”
Harald Dobnig; Stefan Pilz; Hubert Scharnagl; Wilfried Renner; Ursula Seelhorst; Britta Wellnitz; Jurgen Kinkeldei; Bernhard O. Boehm; Gisela Weihrauch; Winfried Maerz.
Arch Intern Med 2008;168(12):1340-1349.
Vol. 168 No. 12, June 23, 2008
Sources: Journal Abstract, JAMA statement.
Written by: Catharine Paddock, PhD