Vitamin D plays a definitive role in the normal growth and upkeep of our body and the quality of our bones. Though classified as a vitamin, it is actually a steroid hormone that is produced by the skin when exposed to sunlight. A vitamin is an organic compound that is essential for the body but is required in very tiny amounts. In that sense vitamin D is a vitamin. However, vitamins are usually not synthesized by the body and for that reason vitamin D is not a vitamin.
Here comes the sun: Vitamin D is a steroid hormone produced by the skin when exposed to sunlight.
Vitamin D is known best for its role in maintaining the calcium balance in our bones. But over the last four decades, scientists have identified many new biological actions for vitamin D apart from bone growth and upkeep, says Anthony Norman, Distinguished professor of biochemistry and biomedical sciences, Emeritus, University of California, Riverside, US. Anthony Norman discovered the existence of vitamin D in 1967 and VDR in 1969.
In a mini review by Norman and Roger Bouillon titled “Vitamin D Nutritional Policy Needs a Vision for the Future" published in Experimental Biology and Medicine, September 2010, the authors say that VDR has been found in at least 38 different tissues in the body. This means vitamin D has a role to play in those many tissues. The review also says that research has shown that Vitamin D plays a role in muscle function and improving muscle strength. It also stimulates the synthesis of anti-bacterial agents in blood cells, and strengthens our immune cells so that they can fight infection more efficiently. It makes our pancreas secrete insulin, and maintains heart muscle function. It also prevents excessive cell proliferation. In other words it may deter various cancers, including prostate, colon and breast cancer, from gaining a foothold.
Given that vitamin D is a hormone that our skin can make when exposed to sunlight you’d think that living in India, where sunshine is abundant, we need not worry about getting enough. This couldn’t be farther from the truth. According to Ambrish Mithal, chairperson of the nutrition working group of International Osteoporosis Foundation, Geneva, and chairman of endocrinology and diabetes division at Medanta, Medicity, Gurgaon, vitamin D deficiency is a growing concern among urban Indians. He says several studies across urban areas, including New Delhi, Lucknow, Mumbai, Chennai, Hyderabad and Tirupati, have found that 60-80% of urban adults have less than 20 ng/ml of 25(OH)D in their blood. Vitamin D deficiency is determined by a blood test, and blood-circulating level of less than 20 ng/ml or 50 nmol/l is considered a deficiency (the normal level should be over 30 ng/ml).
Dr Mithal attributes the high levels of vitamin D deficiency in urban areas to four factors. First, we live largely indoors, especially between 11am and 3pm, the ideal time for skin to soak in the sun for vitamin D production. Second, our clothing choices keep 90% of our body covered even in summer and we need at least 25% of our body to be exposed to the sun in order to make adequate vitamin D. Third, our darker skin tone caused by the higher quantity of melanin requires that we stay in the sun longer than Caucasians to make the same amount of vitamin D. Fourth, Ultraviolet-B (UV-B) rays are essential for vitamin D production and the substantial air pollution in our cities blocks these rays in the sun from reaching us.
Shashank Joshi, consultant endocrinologist at Lilavati Hospital, Mumbai, adds two more factors to this list by saying that unlike the US, our cereals and milk are not fortified with vitamin D. Dr Joshi argues that vegetarianism in India further compounds the issue. According to a The Hindu-CNN-IBN state of the nation survey carried out in August 2006, based on interviews with 14,680 respondents across 18 states, it was found that 31% of Indians are vegetarian and an additional 9% are vegetarians who eat eggs. Vitamin D is naturally found in small quantities in egg yolk and in larger quantities in fish like salmon and mackerel. Cod liver oil provides a whopping dose of 1,360 IUs (international units) of vitamin D in a single tablespoon and has been used to treat and prevent rickets, vitamin D deficiency in babies and children, for decades.
Vitamin D deficiency in its most palpable form expresses itself as rickets in babies, who have legs that bend inwards because of the bowing of their femurs and older children end up with knock-knees. These babies and children also show muscular weakness and an increased tendency for fractures. In adults, vitamin D deficiency is characterized by diffused bone pain, muscular weakness and a fragility of bones with an increased tendency for fractures. Vitamin D deficiency can appear at any age from childhood through adulthood. In its milder forms, the symptoms of vitamin D deficiency are often subtle for many people, says Anoop Misra, director and head, department of diabetes and metabolic diseases, Fortis Hospitals, Vasant Kunj, New Delhi. The only way to know definitively if you are deficient or not is by getting the vitamin D levels in your blood checked annually. If you do take the test and find that your blood levels are below 20 ng/ml, then the typical prescription would be 60,000 IU of vitamin D3 once a week for six-eight weeks followed by 2,000 IUs daily. Ideally, you should get yourself tested three months after first taking the test to confirm that your levels are over 30 ng/ml, says Dr Mithal. Between 20 ng/ml and 30 ng/ml is a range that the physicians call vitamin D insufficient and your levels should at least be over 30 ng/ml. Dr Misra recommends that post-menopausal women and women who have a history of osteoporosis in the family should certainly get themselves tested on an annual basis during the winter months. Given the cost of the test (Rs 1,320 via Metropolis Labs, Bangalore), it may not be practical for everyone to get it done every year.
Dr Misra recommends that everyone try and get more sunshine between 11am and 3pm, ideally 30 minutes a day. Dr Mithal says that while that may be the ideal solution, it isn’t practical and he suggests that all adults take at least 1,000 IUs of vitamin D supplements daily. He recommends that pregnant women can safely take the same dose as well.
Vitamin D supplements come in two forms, vitamin D2 and vitamin D3. Dr Norman says that several papers in the last five years have shown that vitamin D2 is only 60% as effective as Vitamin D3. He says that while the objective is to get your vitamin D levels to be over 30 ng/ml in your blood, the ideal range is probably much higher. While he agrees with Dr Mithal that 1,000 IUs of vitamin D3 should be taken daily, he says that the dose can even be between 2000-4000 IU per day. He says that children can safely take 2,000 IU per day, while infants can take 800 IU per day. Regarding pregnant women, he quotes research data published by Bruce Hollis and his team in the Journal of Steroid Biochemistry and Molecular Biology in March 2007 where they found that pregnant women could safely take 6,000 IU per day. He says since there is a risk of vitamin D toxicity when taken as a supplement, all Vitamin D supplements should be taken under the supervision of a doctor.
Sujata Kelkar Shetty, PhD, writes on public health issues and is a research scientist trained at the National Institutes of Health in Bethesda, US.