In recent months, there has been much debate surrounding vitamin D. Some studies have suggested that a high level of the vitamin benefits our health, while others have reported that there is not enough evidence to make such a claim. Now, a new study from the University of California-San Diego School of Medicine suggests a link between vitamin D deficiency and early death.

Vitamin D is a fat-soluble vitamin that helps regulate the absorption of calcium and phosphorus in our bones, as well as aid cell communication and strengthen the immune system.

Researchers have long associated vitamin D deficiency with poor bone health. In fact, 3 years ago, the US Institute of Medicine (IOM) concluded that low vitamin D is hazardous because it significantly increases the risk of bone disease.

But the health problems associated with vitamin D deficiency do not stop there. Last year, Medical News Today reported on a study led by the University of Kentucky, which indicated that vitamin D deficiency may damage the brain. More recent research claimed that low levels of vitamin D in the first 26 weeks of pregnancy may increase the risk of preeclampsia.

For this latest study, published in the American Journal of Public Health, the UC-San Diego team wanted to see how vitamin D deficiency influenced mortality rates.

Subjects with lower vitamin D levels 'twice as likely to die prematurely'

The researchers conducted a systemic review of 32 studies that analyzed vitamin D, blood levels and mortality rates. The studies involved 566,583 participants from 14 counties - including the US - who were an average age of 55.

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"This study should give the medical community and public substantial reassurance that vitamin D is safe when used in appropriate doses up to 4,000 IU per day," says study co-author Heather Hofflich.

Participants' 25-hydroxyvitamin D levels were assessed. This is the main form of vitamin D found in human blood.

Results of the study revealed that participants with lower levels of 25-hydroxyvitamin D in their blood were twice as likely to die prematurely, compared with those who had higher blood levels of 25-hydroxyvitamin D.

Furthermore, the team found that the 25-hydroxyvitamin D blood level associated with approximately half of participants who were at higher risk of early death was 30 ng/ml - a level that around two thirds of Americans are already below.

According to the National Institutes of Health, children and adults ages 1-70 should have 600 IU (international units) of vitamin D each day, while adults over this age should have 400 IU a day.

But according to study co-author Heather Hofflich, professor in the Department of Medicine at the UC-San Diego School of Medicine:

"This study should give the medical community and public substantial reassurance that vitamin D is safe when used in appropriate doses up to 4,000 IU per day."

However, she adds that patients should have their 25-hydroxyvitamin D blood levels checked annually and consult their doctor before adjusting their vitamin D intake.

Not all researchers are so positive about increasing vitamin D intake. Earlier this year, Medical News Today reported on two studies published in the BMJ, which suggested that there is "no clear evidence" that vitamin D benefits health.

Another study, published in The Lancet Diabetes & Endocrinology in January, also questioned the health benefits of vitamin D, after an assessment of 40 randomized controlled trials revealed that vitamin D supplements are unlikely to reduce the incidence of heart attack, heart disease, stroke, cancer and bone fractures.

Study author Dr. Mark Bolland, of the University of Auckland in New Zealand, commented:

"The main message is that if you are otherwise healthy and active, you are likely to receive enough sunshine to have adequate vitamin D levels and don't need to take vitamin D supplements."