(NaturalNews) People with lower blood levels of vitamin D are more likely to die from all causes, researchers have found.
"We took into account 30 different variables - including age, weight, diabetes, cholesterol, high blood pressure, whether they exercise, smoking - and we found that low vitamin D levels, independent of all these other risk factors for heart disease, predicted an increased risk of dying from any other cause. So we found a new risk factor for death," said study author Erin Michos.
Michos and colleagues from Johns Hopkins School of Medicine and Albert Einstein College of Medicine analyzed vitamin D and mortality data from more than 13,000 adults over the age of 19 who had participated in the third National Health and Nutrition Examination Survey (NHANESIII). The NHANESIII participant pool had been carefully selected to give an accurate representation of the general U.S. population, although it might not be representative of other countries.
The vitamin D blood levels of all participants had been tested once between 1988 and 1994. Because the body synthesizes vitamin D upon exposure to sunlight and blood levels consequently tend to be higher in the summer, participants from southern states had their blood taken in the winter, while northern participants had theirs taken in the summer. This was done to ensure similar conditions for assessing overall deficiency.
Participants were divided into four groups, based upon vitamin D status. The researchers then used the National Death Index to determine which participants had died by the year 2000, as well as their cause of death.
A total of 1,807 study participants had died by the year 2000, 777 of them (43 percent) from cardiovascular disease. Among these, 76 percent had died from atherosclerotic cardiovascular disease. The second most common cause of mortality was cancer, accounting for 23 percent of deaths.
The researchers found that participants in the quartile with the lowest vitamin D levels (an average of 17.8 nanograms per liter) were 26 percent more likely to have died than participants in the highest quartile. Altogether, the researchers estimated that vitamin D levels could account for up to 20.6 percent of mortality risk.
Being in the lowest vitamin D quartile was also associated with a 70 percent increase in death rate from cardiovascular causes. This correlation dropped to close to 26 percent when the researchers adjusted for other cardiovascular risk factors, however, and was no longer statistically significant. According to Michos, more research is needed to determine if vitamin D plays a role in heart health.
"We also need to prove if we give additional vitamin D, will it prevent a heart attack?" she said.
Initially, researchers also found a correlation between low vitamin D status and increased cancer mortality. This association quickly vanished when only a few complicating factors were adjusted for, however. No association was found between vitamin D levels and death from infectious diseases.
The researchers admitted that the study could not determine if vitamin D deficiency was actually a cause of early death, or if it was merely a marker for other factors. But they noted that a stronger relationship between vitamin D levels and mortality was seen in participants without cardiovascular disease or risk factors such as diabetes, hypertension or male sex. The researchers interpreted this as evidence "against low vitamin D levels being only a marker of poor general health."
"If a causal relationship exists, [vitamin D] deficiency may play a role before cardiovascular disease is established," they wrote.
The study was funded by the National Institutes of Health and published in the Archives of Internal Medicine.
Also known as the "sunshine vitamin," vitamin D plays a critical role in the development and maintenance of bones and teeth. Deficiency has long been known to lead to bone deformities in children, and osteoporosis and other bone disorders in adults. Recent research has also suggested that low levels of vitamin D may increase the risk of immune disorders, cancer, high blood pressure and diabetes.
The average light-skinned person can get all the vitamin D they need from just 15 minutes of sun per day on the face and hands, while a darker skinned person may need up to twice as much. In extreme northern or southern latitudes, however, the weaker sun may not provide sufficient ultraviolet radiation for adequate vitamin D synthesis, particularly in winter. For this reason, many grain and dairy products are regularly fortified with vitamin D.
Nevertheless, a number of studies suggest that vitamin D deficiency remains widespread, with 53 percent of women and 41 percent of men in the United States testing for less than 28 nanograms per milliliter in their blood. In the mortality study, deficiency was more common in those who were older, female, nonwhite, diabetic, smokers, less physically active, had a higher body mass index, or who were tested in the winter.
Levels of 30 nanograms per milliliter or more are considered adequate, levels below 20 nanograms per milliliter are considered deficient, and levels in between are considered insufficient.
Researchers are split on how much dietary vitamin D people should ingest to avoid deficiency. While 400 IU per day appears to be sufficient to ward off bone disorders, levels of 1,000 IU per day are now recommended by many experts as necessary for protecting against cancer and other diseases.
The British National Health Service (NHS) recommends that people try to get as much of their vitamin D as possible from sunlight and dietary sources.
"In the absence of definitive research indicating that taking extra vitamin D can reduce risk of death, it is advisable to try and maintain vitamin D levels naturally through diet and sensible sun exposure," the NHS said.