You probably remember from high school biology that Vitamin D is good for your bones. But did you know recent research has shown that it can also keep cancer and heart disease at bay? And if you thought vitamin D deficiency was only a problem for temperate climates, think again.

Vitamin D is the only vitamin you can get from either your diet or by your skin synthesizing it in the sun. When exposed to ultraviolet light with wavelengths less than 315 nm (in sunlight, our natural source of UV, this translates to UVB), a cholesterol derivative in skin cells absorbs energy and goes through a series of reactions to form an active form of vitamin D. The level of an intermediate inactive form in the blood, 25-hydroxyvitamin D, or 25(OH)D for short, is the most reliable indicator of vitamin D status.

Hours of  video games and drinking sodas instead of milk may be putting children's bones at risk from low vitamin D levels. A new study shows more than half of otherwise healthy children have low vitamin D levels in their blood, which may put them at risk for bone diseases, says a WebMD report. The low vitamin D levels may reflect current trends of children spending less time outdoors and drinking less milk than in the past, it said In the study, published in the American Journal of Clinical Nutrition, researchers analyzed blood levels of vitamin D in 382 healthy children from ages 6 to 21. They found 55% of the children had lower than recommended vitamin D levels. "Vitamin D deficiency remains an under-recognized problem overall, and is not well studied in children," says researcher Babette Zemel, PhD, a nutritional anthropologist at Children's Hospital of Philadelphia, in a news release.

Recent research has highlighted the paradox of low levels of the sunshine vitamin in the Indian population. Says Dr C V Harinarayan, Head, Dept of Endocrinology and Metabolism, Sri Venkateswara Institute of Medical Sciences, Tirupati, “We are deficient and insufficient in vitamin D status as a population despite abundant sunshine!”
What’s more, a distressingly low level of the vitamin seems to be the norm. In Tirupati and surrounding villages, for example, Harinarayanan found almost 70 % of the population has low levels of vitamin D – urban women had ~17 ng/ml 25(OH)D and rural women had ~21 ng/ml.

Similarly, Ravinder Goswami and colleagues from AIIMS found more than 90 % of their sample of apparently healthy people in Delhi had even lower levels of 25(OH)D, on average, less than 10 ng/ml. Based on much recent research on vitamin D, many believe 25(OH)D levels should be at least 30 ng/ml.

So what happens if we don’t get enough of this vitamin? For one, your bone health takes a nosedive.

Explains Dr Harinarayanan, “The calcium absorptive performance of the gut is a function of 25(OH)D status of an individual. Low vitamin D impairs dietary calcium absorption and adversely affects bone mineralization.”
In other words, you can guzzle all that calcium-laden milk and yogurt you want, but it may not do your bones much good if you don’t also get some sunlight, because vitamin D and calcium work synergistically.

Role in cancer
But more than bones are at stake. Mounting evidence reveals vitamin D’s role in other areas, including insulin activity, resistance to cancers like prostate, breast and colon cancer and even cardiovascular health. Its link to cancer may be mediated through the 200 or so human genes that contain vitamin D response elements. Many code for proteins important in the regulation of cell proliferation and differentiation.

With suboptimal vitamin D status, these activities are impaired. The latest work to show a vitamin D-cancer link appeared in June in American Journal of Clinical Nutrition. A four-year study following 1179 postmenopausal women found that those receiving a supplement of calcium and vitamin D had lower risks of cancer than those receiving a placebo.

Heart protection
And while the exact mechanism for vitamin D’s heart protective effect is still unknown, more evidence for such an effect came in a paper last month in Archives of Internal Medicine. Using data on 7186 males and 7092 females, one of the largest datasets for a vitamin D study, researchers found lower vitamin D levels were significantly associated with increased cardiovascular disease, diabetes and hypertension than were higher levels of vitamin D (more than 37ng/ml 25(OH)D).

These researchers have joined a chorus of voices urging a fresh look at recommendations of optimum levels of vitamin D. Current recommended levels in the US, for example, are in the range of 200 international units (IU) for children to 600 IU for people over 70. But while these levels may be sufficient for optimum bone health and to prevent rickets, researchers in the field say they are woefully inadequate in terms of minimising the prevalence of heart disease risk factors. Most researchers feel people should strive to get at least 1000 IU of the vitamin daily.
The Indian Council of Medical Research has no recommendations issued for vitamin D. 

The list of foods rich in vitamin D is all too short: egg yolks, fish, liver oils such as cod liver oil, some wild mushrooms and, according to Dr Harinarayan, drumstick leaves. For most us, 90% of our vitamin D comes from sunshine.

And herein lies one problem. The lifestyles of most urban Indians keep them indoors most of the time; being blessed with abundant sunshine is of little use if we don’t venture out into it. Add to that the national obsession with ‘fair’ skin, so that most people, especially women, are loath to expose their skin to the sun at all for fear of turning ‘dark’. This explains why rural women often have higher vitamin D levels than urban women – likely because of greater exposure to the sun.

But why do even rural Indian women have lower than ideal levels of the sunshine vitamin? Blame it on melanin. Too much sun can be a bad thing – it can degrade folate, an essential, water-soluble B vitamin. To protect us from this damaging effect of ultraviolet rays, Nature endowed people in sun-kissed climes with natural UV protection: melanin, the pigment that gives us our ‘wheatish complexion’.

But, effective sunscreen that it is, melanin also interferes with the formation of vitamin D in our skin. This means that brown skin needs 5-10 times as much sunshine to make the same amount of Vitamin D as light skin.
But before you brace yourself to broil in the sun, consider that the key is sensible sun exposure. A light skinned person, in say, Boston, USA, needs 5-15 minutes of sunlight three days a week for optimum Vitamin D levels.
In figuring out how much of sunshine you need, remember that we enjoy greater sunshine in India but we also need greater exposure than light skins. Also remember that exposing your full body for just 2 minutes would get you the same vitamin D dose as exposing just a bald head and neck to the sun for 20 minutes. So you can either offer up your arms, legs and face to the sun for approximately an hour, or if you can, do the full monty for about 6-10 minutes. Get your daily dose of D, then slather on the sunscreen if you need to. Now go on, let the sunshine in.