itamin D, also called the sunshine hormone, is essential for the development of teeth and bones. Besides being involved in the metabolism of calcium and phosphorus, it also has a role in the inflammatory response, glucose and lipid metabolism and cardiac and vascular regulation.

Study reports suggest that approximately one billion people in the world are affected with vitamin D deficiency, and around 50 percent of the global population has vitamin D insufficiency. A meta-analysis of vitamin D deficiency in Pakistan from 2008-2018 showed that 58.17 percent of the population was vitamin D-deficient and 26.65 percent insufficient in vitamin D. Sindh reported the highest numbers.

Vitamin D is derived naturally from two main sources: diet and the effects of ultraviolet B (UVB) from sunlight on the conversion from the steroid precursor, 7-dehydrocholesterol, in the skin. The best food sources of vitamin D are oily fish, including salmon, mackerel and sardines. Other sources include egg yolks, red meat, and liver. Fortified foods – such as formula milk and breakfast cereals are also good sources. One teaspoon of cod liver oil contains 1,360 IU. Milk (240 ml) contains 100 IU. Calcium along with vitamin D is essential to keep bones healthy. Calcium-rich foods include milk, yoghurt, cheese, leafy vegetables, beans and oranges. A 240 ml glass of milk contains 300 grams. A medium orange fruit contains 60 gms of calcium. Non-dairy milk (soy, almond, oat) also are rich in calcium.

Vitamin D deficiency can be caused by inadequate dietary intake, lactose intolerance or poor exposure to sunlight (inadequate ventilation in the house, fully covered dresses, night duties).

Nutritional rickets is caused by low intake of calcium, vitamin D or phosphorus, Vitamin D/ calcium deficiency being the most common cause. Rickets is characterised by bone pain, and soft and weak bones that can lead to bone deformities. Widening of wrists, deformities of ribs and bowing of legs occur in severe deficiency. Osteomalacia in adults causes softening of bones.

Vitamin D is needed for active calcium absorption from the intestines. When Vitamin D is deficient, calcium is mobilised from bones and phosphorous is excreted from the kidneys. These events result in phosphate deficiency. The generalised hypophosphataemia also affects other tissues, causing muscle weakness and pain.

How to diagnose rickets?

Low serum vitamin D3, raised serum alkaline phosphatase, low calcium/ phosphate with clinical signs are suggestive of rickets. Prolonged deficiency is reflected in bone changes identified on X-ray of wrist/ knees.

Vitamin D is needed for active calcium absorption from the intestines. When Vitamin D is deficient, calcium is mobilised from bones and phosphorous is excreted from the kidneys. These events result in phosphate deficiency. The generalised hypophosphataemia also affects other tissues, producing muscle weakness and pain.

Who is at risk of developing vitamin D deficiency?

Exclusively breastfed infants are at risk as mother milk is deficient in vitamin D. Also, infants of mothers with known vitamin D deficiency are at risk of developing nutritional rickets. Both mother and infant must be started on with supplements for at least six months. As people age, the skin cannot synthesise vitamin D efficiently, and the kidneys have difficulty converting vitamin D to its active form. Obese individuals have low serum levels of 25 (OH)D because of deposition in body fat compartments. Also, people with certain medical conditions like pancreatic enzyme deficiency, Crohn’s disease, cystic fibrosis, coeliac disease, or with surgical removal of any part of the stomach or intestines affecting absorption of lipids tend to absorb less vitamin D.

How to prevent vitamin D deficiency?

The WHO recommends that very low-weight infant be given vitamin D supplements at a dose ranging from 400 IU to 1,000 IU per day until six months of age. The daily requirement of vitamin D in men of age 65 years and above and post-menopausal women is 800 IU (20mcgs). 90 percent of hip fractures in this age group are caused by falling due to weak bones. Hence, daily vitamin D intake is important in this age group.

The optimum requirement for pre-menopausal women and young men with osteoporosis is 600 IU (15mcgs).

There are many oral drop formulations available in the market. Intramuscular injectables are also available, but self-medication is discouraged. Doses as per age and underlying medical conditions (like pregnancy, lactation, osteoporosis) have to be calculated by consulting a physician before administration to avoid adverse effects. Overdosing may cause metallic taste, headache, nausea, vomiting, kidney function impairment and vascular calcification.

Vitamin D supplements are usually complimented with calcium. The WHO recommends 300-400 mg/day of calcium for infants, 500 mg/day in children aged 1–6 years, 700 mg/day in children aged 7–9 years and 1,300 mg/day for adolescents. 1,000mg is recommended for pre-menopausal women and men. For post-menopausal women, a higher dose of up to 1,200 mg/day is recommended. This is the total calcium required through diet and supplements. Calcium supplementation is recommended during pregnancy to reduce the risk of pre-eclampsia. The recommended dose is 1,500-2,000 mg/ day in divided doses, preferably to be taken with meals. However, calcium supplements should not be taken with iron supplements as it decreases iron absorption. Also, medicines used to treat acidity decrease the absorption of calcium. Hence these medicines should be taken at different times.

Does dietary calcium cause kidney stones?

Excess of calcium in the diet doesn’t cause kidney stones. However, calcium in supplements increases the risk by raising the calcium excreted in urine.

The writer is a consultant family physician [MBBS, FCPS, MRCGP(INT)], www.oladoc.com