While scientists have known for decades that deficiency leadsto bone diseases like rickets, more recently they have foundconnections between low vitamin D levels and a wide range of otherillnesses, including cancer, autoimmune disorders and caradiovasculardisorders.
The human body creates vitamin D through exposureto sunlight, and yet some of the sunniest parts of the world have thehighest rates of vitamin D deficiency. Several factors have contributedto dangerously low vitamin D blood levels among people in the MiddleEast, Africa and Asia.
Healthy bones depend on vitamin D, says Ambrish Mithal of the .
"VitaminD is what absorbs calcium into our body and helps it reach the bone.Vitamin D deficiency, therefore, results in weak bones and bones thatare soft, that will bend and break."
Getting enough vitamin D should be relatively simple.
"Themajor source of vitamin D is sunshine," Mithal says. "We make vitamin Dunder the influence of UV rays that we get in the sunlight. We make itin our skin."
Butsome of the world's sunniest regions have the highest rates of vitaminD deficiency. That's the finding of a recent from the, which reviewed research doneover the past three decades. Mithal is a coauthor of that report.
"VitaminD deficiency is a global phenomenon. But certain parts of the world,they're prone to severe vitamin D deficiency - for example, South Asia,like India, or Middle East, like Lebanon. There have been studies fromthese areas which have shown that almost 80 percent, or maybe evenmore, of the urban population is significantly vitamin D deficient."
He points to several factors to explain why people who live in sunny areas still may not get sufficient vitamin D.
"Thosewho live closer to the equator are actually less prone to vitamin Ddeficiency, but at times this, can be overshadowed by other factorslike skin pigmentation, less outdoor activity and more skin cover withclothes," Mithal says.
Vitamin D expert Michael Holick, of theBoston University Medical Center, explains why people with darker skingenerally have lower levels of the nutrient than lighter-skinnedpeople, even in the same country.
"The major reason is thattheir melanin, which protects their skin from excessive exposure tosunlight, also prevents them from making vitamin D," he says. "Weshowed that African-Americans need to be exposed three to five timeslonger to sunlight to be able to make the same amount as a whiteperson."
Another coauthor of the vitamin D review, Ghada El-HajjFuleihan, describes how people in the Middle East can spend timeoutdoors without absorbing enough vitamin D.
"In these, theMiddle Eastern countries, people tend to follow a very much moreconservative clothing style, in a large proportion of subjects. And theother thing is that with modernization, women who do not follow theconservative clothing style use sunblock. Sunblock with sun protectionfactor as low as six and eight can completely block the ability of theskin to make vitamin D."
El-Hajj Fuleihan, of the AmericanUniversity of Beirut Medical Center, says this may explain why women ingeneral have lower vitamin D levels.
Thereis new concern about vitamin D deficiency because, as Michael Holickexplains, recent medical discoveries show it may be much more dangerousthan previously thought.
"What we haven't appreciated untilabout the past decade is that vitamin D seems to be important forreducing risk of many chronic illnesses that span anywhere fromautoimmune diseases like type 1 diabetes, multiple sclerosis,rheumatoid arthritis, to infectious diseases like tuberculosis andinfluenza, reduces risk of heart attack, stroke and most importantly,reduces risk of deadly cancers."
Peoplecan get more of the nutrient in their diet. In the United States andother countries, some foods are fortified with vitamin D. But Holicksays that's generally not enough.
"Children probably need athousand units of vitamin D a day. Teenagers and adults need twothousand units of vitamin D a day to satisfy their requirement? Youcannot get an adequate amount of vitamin D to satisfy your body'srequirement from your diet."
So, he and other experts like Ghada El-Hajj Fuleihan, now recommend spending a little more time in the sun.
"Weare fully aware of the risk of skin cancer with sun exposure butsuggest that there may be a happy compromise and that maybe the first10 minutes or so three times a week? let the skin get some ability tomake vitamin D, and then put the sunblock on."
In addition, she says, those who spend their days indoors should take a vitamin D supplement.