Vitamin D (25-OH)

A below normal level indicates vitamin D deficiency, it can occur in conditions such as lack of exposure to sunlight, dietary deficiency of vitamin D, liver and kidney diseases, poor food absorption in cystic fibrosis and Crohn’s disease, and in patients who have undergone gastric bypass surgery. Along with that, using certain medicines such as phenytoin, phenobarbital, and rifampin, etc. can cause vitamin D deficiency. These reduced levels of vitamin D can also be observed in infants who only feed on breast milk. Such infants can be given formula milk, as it is fortified with vitamin D. An increased level of vitamin D is called hypervitaminosis D or vitamin D toxicity. This is most commonly caused by taking too much vitamin D and can result in increased calcium levels in the body (hypercalcemia). It can also cause kidney and blood vessel damage.

Inform the doctor about the medications you may be taking. No other specific preparations are usually required before this test.

Vitamin D 25 (OH) should be tested in individuals who are undergoing therapy to prevent or treat osteoporosis, patients having signs and symptoms of low calcium level (hypocalcemia) or high calcium level (hypercalcemia). It should also be done in patients with cystic fibrosis, Crohn’s disease, and with gastric bypass surgery, patients receiving vitamin D therapy who do not demonstrate clinical improvement. Along with that, these tests can be done in elderly people, especially those with minimal exposure to sunlight, children and adults with suspected rickets and osteomalacia, respectively, and infants who are exclusively breastfed.

Additional tests which can help establish vitamin D deficiency are: 24-hour urine calcium Parathyroid hormone Total or bone alkaline phosphatase level Serum calcium and serum phosphorus level Radiological test

There can be various factors that can affect 25-OH vitamin D levels, some of them are explained below: Seasonal variation: Ideally, all samples should be collected in one season. The reason being, there can be seasonal variation in 25 (OH) vitamin D level, with values being 40-50% lower in winter than in summer. This can affect the absorption rate of Vitamin D. Age: Older adults have a reduced level of 7-dehydrocholesterol, so they cannot synthesize 25(OH) vitamin D. Along with that, the production of active hormone (1,25 dihydroxyVitamin D3) gets reduced by their kidneys. Skin color: Melanin in the darker skin reduces the ability to produce 25(OH) Vitamin D from sunlight exposure, as it absorbs the sunlight. Body mass index/nutrition: Obese individuals (body mass index >30 kg/m2) are deficient in Vitamin D, as Vitamin D is fat-soluble. This is because it gets sequestered in the fat and not able to circulate. As a result, the rate of absorption of Vitamin D remains low in obese patients as compared to other healthy individuals. Certain medicines like phenytoin (seizure drug), phenobarbital, and rifampin, cholestyramine, orlistat, steroids, stimulant laxatives can reduce Vitamin D level. Other than these, Vitamin D can also get influenced by sunlight, latitude, sunscreen use, and hepatic function.

Osteomalacia is softening of the bones due to demineralization (the loss of mineral) and most notably by the depletion of calcium from bone. It is a characteristic feature of vitamin D deficiency in adults. Osteomalacia can also be caused by poor dietary intake or poor absorption of calcium and other minerals needed to harden bones.

Vitamin D is derived from endogenous sources and exogenous sources. Endogenous sources are produced in our body when our skin is exposed to sunlight. Whereas, exogenous sources can only be derived from other sources, as they are not produced in our bodies. Dietary sources of vitamin D include fish, eggs, fortified dairy products, and dietary supplements.

Osteoporosis is a condition of fragile bones with increased susceptibility to fracture. Vitamin D and calcium deficiency are one of the leading causes of osteoporosis. Other risk factors can be genetics, lack of exercise, personal history of fracture as an adult, cigarette smoking, excessive alcohol consumption, history of rheumatoid arthritis, low body weight, and family history of osteoporosis. Usually, osteoporosis does not manifest itself until bone fractures occur. X-rays and bone mineral density test can help diagnose osteoporosis.