We’ve all known that vitamin D is the “sunshine vitamin” the skin conjures up when exposed to sunlight. And that Vitamin D-deficiency causes rickets, osteoporosis (weakened bones), heart disease, diabetes, infections such as tuberculosis and cancers of the colon, breasts, ovaries and prostate. And that you need as little as 30 minutes of sunshine a day to make enough to prevent disease and stay healthy.
Still, nine in 10 people have vitamin D deficiency in India, and here’s why.
To begin with, the skin needs to be uncovered for ultraviolet (UV) B radiation with a wavelength of 290–320 nanometers to penetrate it and convert cutaneous 7-dehydrocholesterol to vitamin D, which is then stored in the liver and fat. Apart from clothes, several other factors stop the sun from reaching the skin’s surface.
As sunlight passes through the atmosphere, the ozone, water vapour, oxygen and carbon dioxide in it absorbs all UV-C and almost 90% of UV-B radiation. UV-A radiation is less affected by atmospheric gases, so most of the UV radiation reaching us is UV-A with a small UV-B component.
Then, there is cloud cover, smog, dust and pollution that reduces UV energy by more than half. UV-B radiation cannot penetrate glass, so exposure to sunshine indoors through a window does nothing to boost the vitamin D stores in your body. You also lose out on the elusive vitamin because UV-B radiation is highest in the early afternoon in the summer months, which is the period when most of us look for reasons not to step out.
People who are overweight, obese or are older than 65 need more sunlight, as do people with dark skin that is high in melanin — the pigment that gives skin and hair its colour — that makes it harder for the skin to absorb UV-B. Correctly applied sunscreen lowers UV-B absorb by 90%.
These factors is perhaps why researchers recommend 30 minutes of sun exposure between 10 am and 3 pm for white-skinned people two to three times a week, but three to six times his amount for people with dark skin, including south Asians.
And there are enough data from India to show most of us are not getting enough sun. A study in the journal Nutrients reported in February said Vitamin D deficiency had reached “epidemic proportions all over the Indian subcontinent”, with a prevalence of 70%–100% in some populations. The data has changed little since 2008, when researchers from the All India Institute of Medical Sciences reported in the British Journal of Nutrition that 90% of apparently healthy Indians living in India had subnormal levels of Vitamin D.
People in urban areas are the most deficient. Initial findings of 481 healthy women from seven middleclass and upper middleclass government-residential neighbourhoods in Delhi shows only 5.84% women had healthy levels (30-100 µg /ml) of vitamin D. Of them, 26.57% were severely deficient with levels less than 20 µg /ml, while the majority (67.59%) had insufficient amounts (21-29 µg ml) of the vitamin. The study, led by Dr Anoop Misra, chair of the Fortis C-DOC Centre, also found that over 70% women were obese (BMI more than 25 kg/m2) and 20% were overweight (BMI between 23 and 24.9 kg/m2), with less than 10% having a healthy weight. Being overweight interferes with vitamin D formation.
India fares badly in comparison to the rest of the world. Worldwide, one in seven people — roughly 1 billion — have inadequate levels of vitamin D.
Currently, there’s scientific debate about how much vitamin D we need each day. For adults with little exposure to sunlight, Indian Council of Medial Research recommends a daily supplementation of 400 international units, and 600 IU for people over 65 years, but the new US Institute of Medicine guidelines recommend increasing intake to 600 IU per day for children and adults, and 800 IU for people over 70 years.
To get 400 IU of vitamin D, you have to eat 200 gm of an oily fish every day, which easily makes popping a multivitamin a more doable option. Supplements contain two forms of vitamin D -- vitamin D2 (ergocalciferol, or pre-vitamin D) and vitamin D3 (cholecalciferol), with the latter being chemically indistinguishable from the vitamin D produced in the body.
In the absence of food fortification in India, the best way for us to get enough is by taking a supplement, but the amount in most multivitamins (400 IU) is too low for people deficit in the nutrient. If you’re deficit, you may need a separate vitamin D supplement, more so if you don’t like sunny weather all that much.