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Resource centre on India's rural distress
 
 

Face the sun by Swetha Manian

Vitamin D deficiency on the rise; tests to identify it inaccurate

AIR-CONDITIONED homes and offices and AC vehicles with dark glasses that protect from UV rays are now integral parts of our lifestyle. But by avoiding sunlight by using sunscreens and umbrellas one denies the body an important nutrient—vitamin D.

All forms of life exposed to sunlight can produce this vitamin, which plays a vital role in the growth and maintenance of bone health by enabling the absorption and metabolism of calcium and phosphorus. Low levels of vitamin D have also been linked to rickets (soft and deformed bones), osteoporosis, cancers, multiple sclerosis and Parkinson’s disease.

“Low level of the vitamin also raises the level of parathyroid hormone in the body. The hormone mobilises calcium from the bones, worsening bone health and causes one to lose phosphorus through urine,” says Sorna Velayudham, former professor of obstetrics and gynaecology at the Tamil Nadu Medical Services in Chennai. Furthermore, “Activation of parathyroid hormone can lead to secondary hyperparathyroidism,” adds Madhavi Garimella, endocrinologist with Medical Associates of Northern New Mexico in the US.

She calls this vitamin “the vitamin of the decade”. In her words, “we have become more aware of this vitamin and its deficiency in the past one decade”. Doctors are reporting higher number of patients with vitamin D deficiency.

But vitamin D cannot be measured directly in the blood. It rapidly changes into another form in the liver so its metabolite, 25-hydroxyvitamin D—25(OH)D—is measured. This is done either by using the immunoassay or chromatographic techniques which need a standard to compare results.

But there is no standard. Recently, researchers at VU University Medical Center in Amsterdam assessed six assays for the vitamin and found most immunoassays were inaccurate. Also countries use various methods to measure the vitamin levels. In India, levels of 25(OH)D are analysed in terms of its inverse relationship with parathyroid hormone levels and association with reduced bone mineral content.

Renewed hope

Now to take care of the inaccuracies, researchers at the National Institute of Standards and Technology at Maryland in the US have developed a Standard Reference Material—SRM 972. It will help determine the level of the metabolite in blood. “In the absence of certified reference materials for 25(OH)D, establishing the accuracy of assays has remained elusive,” write researchers in a recent issue of Analytical Chemistry. It is the first certified material for vitamin D metabolite. “Our goal was to provide a way to evaluate the accuracy of the methods, independent of which method is being used,” says Karen Phinney, lead researcher.

The way out

The Endocrine Society Clinical Guidelines states that without vitamin D, only 10-15 per cent of dietary calcium and 60 per cent of phosphorus is absorbed. With optimal levels, these numbers can go up to 30-40 per cent and 80 per cent respectively. The guidelines also state that vitamin D levels above 30 nanogram (ng) per ml are optimal, anything below 20 ng/ml is deficiency and 21-29 ng/ml is considered insufficient.

The reason for this deficiency, apart from lifestyle, says Garimella, is change in food and dietary preferences over the past few years. Velayudham agrees, “People change their dietary preferences but do not realise that they should make up for what is lacking. Milk is a great source of this vitamin. But people are switching to dairy-free diet,” says Velayudham.

People with low vitamin D level are advised to take supplements. For people who do not want to take supplements, exposure to sun and consumption of vitamin D-rich food are sufficient. “It is neither difficult nor expensive to obtain optimal vitamin D levels in our body. All one requires is some exercise and sunlight,” says Garimella. A ‘pinkish tinge on the skin’ is an indication of optimum exposure to sunlight for activation of vitamin D in the body, say the Endocrine Society Guidelines.