Vitamin D is often called the “sunshine vitamin” — and with good reason. Our bodies can produce it when exposed to sunlight, and it seems to play an essential role not only in bone and mineral metabolism, but in immunity, and even mood regulation. Even though Vitamin D can be produced in the body, there seems to be widespread deficiency of this vitamin at a global level, and even more so in the countries such as India that have plenty of sunshine.
Understanding Vitamin D
Vitamin D is a fat-soluble vitamin along with Vitamin A, Vitamin K and E. Unlike water- soluble vitamins such as Vitamin B, fat-soluble vitamins are less easily excreted in urine and are more likely to cause toxicity due to poor excretion in urine if taken in larger than required levels.
Vitamin D2 (ergocalciferol): Generally, vitamin D levels are very poor in vegetarian diets. It is found in small amounts in almonds and mushrooms.
Vitamin D3 (cholecalciferol): Found in large concentrations in animal products such as fish, egg, liver etc.
Once in the body, Vitamin D2 and D3 are converted into calcidiol (25-hydroxyvitamin D) in the liver, the form measured in blood tests, and then into calcitriol in the kidney, which is the active molecule in the body. The complexity of this pathway partially explains why Vitamin D levels are low even though it can be produced in the body.
Daily requirement of Vitamin D in children and adults is 600-800 IU/day; in the elderly population, it is around 800-1000 IU/day depending on the risk profile, and in pregnant women, it is 1000-1200 IU/day.
These levels are identified through a consensus by expert groups, based on the absorption of calcium from the intestine, increases in parathyroid hormone levels as an expression of altered bone mineral metabolism, and by increased fractures in the elderly.
Deficiency definitions vary in different guidelines, however according to a consensus statement, the following blood levels have been identified
Deficiency – <20 ng/dl
Insufficiency – 21 – 30 ng/dl
Sufficiency – 31-75 ng/dl
Toxic levels – > 100 ng/dl
Epidemiology of deficiency
Vitamin D insufficiency is common globally. In India, vitamin D levels <20 ng/dl are present in 30 – 50% population, higher than what is seen in developed countries such as the U.K. or U.S. A probable reason for this is poor exposure to sunlight, atmospheric pollution, vegetarian diets and lack of fortification of dairy products in the country.
Research over the past few decades has expanded our understanding of the importance of Vitamin D far beyond the skeletal system. Vitamin D receptors are found in almost all human tissues, indicating its influence on multiple organ systems. These extra-skeletal effects impact immunity, cardiovascular health, metabolic function, and even mental well-being. However, in extra-skeletal effects, there is no causal association established between Vitamin D deficiency and these diseases.
Vitamin D deficiency, however, has a well-established association with poor balance and muscle weakness. Many studies have found associations between falls and low Vitamin D levels in older adults.
Vitamin D also plays a role in modulating both innate and adaptive immunity. Deficiency has been linked to increased susceptibility to infections, including respiratory tract infections and tuberculosis. Vitamin D deficiency has also been implicated in cardiovascular disorders and metabolic disorders such as diabetes mellitus. However, these associations have not yet been shown to be causatively linked, and further research may be needed.
Treatment of Vitamin D deficiency
In many countries, mandatory food fortification has been noted to be a cost-effective strategy to control widespread vitamin D deficiency. But this strategy mandates widespread availability of testing for Vitamin D levels across the country to detect toxicity, which is currently not available in India.
Testing and treating is an alternative strategy. A follow-up blood test is typically done 2–3 months after starting supplementation.
This article was first published in The Hindu’s e-book Care and Cure.
(Kurien Thomas is senior consultant, physician and clinical epidemiologist, Naruvi Hospitals, Vellore. kurien.t@naruvihospitals.com; Pranita Vanjare is consultant, geriatrics and internal medicine, Naruvi Hospitals, Vellore. pranita.r@naruvihospitals.com)
