Higher vitamin D levels reduce risk of heart attack and death.
Two new studies add to what one researcher called an "overwhelming" accumulation of evidence that maintaining adequate vitamin D levels is important to your health—and that those levels may be higher than current official recommendations. In one study, men with low blood levels of vitamin D were at twice the risk of heart attack as those getting plenty of the "sunshine vitamin." Just days later, a second report was published showing that individuals with lower blood levels of vitamin D had an increased risk of death in general and from cardiovascular causes in particular.
Current recommended Daily Reference Intakes (DRI) for vitamin D range from 200 IU for children and adults age 50 and under, to 400 IU for men and women ages 51 to 70, to 600 IU for those over age 70. Recent research, however, has suggested that higher intakes may be required for optimal health, including vitamin D's bone-building benefits. Some experts have called for significant increases in recommended doses, and for balancing the skin-cancer risks of sun exposure against the benefits of vitamin D that the body makes naturally in sunlight.
Investigators in the first study, led by epidemiologist Edward Giovannucci, MD, ScD, of the Harvard School of Public Health, noted that deaths from cardiovascular disease increase at higher latitudes and during winter months. That's consistent with an adverse effect of lower vitamin D levels among people with less sun exposure.
Dr. Giovannucci and colleagues looked at data on 18,225 men, ages 40 to 75, in the Health Professionals Follow-up Study who were initially free of diagnosed cardiovascular disease. Only 23% of participants had vitamin D blood levels considered normal—30 nanograms per milliliter (ng/mL) or higher. That's not so unusual, however; a recent expert panel estimated that 50% to 60% of older North Americans are lacking in vitamin D.
Over a 10-year span, 454 of the men in the large study group suffered nonfatal myocardial infarctions (MI—heart attacks) or died of coronary heart disease. Researchers compared those cases to almost twice as many healthy men. After adjusting for age, smoking, diet and lifestyle factors. men lowest in vitamin D (15 ng/mL or less) were 2.42 times more likely to suffer an MI than those with adequate levels. After further adjustment for a wide range of factors including family history of MI, physical activity and cholesterol, the low-vitamin D group still had more than double the risk for MI. Even men with intermediate vitamin D levels (22.6 to 29.9 ng/mL) had a 60% greater MI risk.
The association between low vitamin D and increased risk of fatal heart disease was even stronger, but larger numbers of cases would be required to confirm this link.
Writing in the Archives of Internal Medicine, Dr. Giovannucci and colleagues concluded that their findings "add further support to the belief that the current dietary requirements of vitamin D need to be increased to have an effect on circulating vitamin D levels substantially large enough for potential health benefits."
Hard on the heels of those findings, the same journal published a study led by Harald Dobnig, MD, from the Medical University of Graz, Austria, of 3,258 patients, average age 62, undergoing coronary angiography testing. During about 7.7 years of follow-up, 737 (22.6%) of this group died, including 463 (62.8%) who died of cardiovascular causes. Death rates from any cause and from cardiovascular causes were higher among the half of the patients with lower vitamin D levels. The same trend was seen among the quarter of the patients lowest in another measure of the body's vitamin D.
Low vitamin D levels were also linked with markers of inflammation such as C-reactive protein, as well as signs of oxygen-related damage to cells.
"Apart from the proved effects that vitamin D has on bone metabolism and neuromuscular function, appropriate serum levels (that may also be higher than in the present investigation) are associated with a decrease in mortality," the researchers concluded. "Although not proved, it seems possible that at least part of this effect may be due to lowering of a risk profile promoting atherosclerosis [narrowing of the arteries] and preventing cardiovascular end points."
Dr. Dobnig cautioned that the results don't prove low vitamin D levels are unhealthy, "but the evidence is just becoming overwhelming at this point." In an AP interview, he noted that scientists used to think vitamin D was important only for preventing rickets and strengthening bones. "Now we are beginning to realize that there is much more to it."