Vitamin D: An Essential Micronutrient for Bone Health

Vitamin D for Bone Health

Abstract

Vitamin D is an essential micronutrient in children for bone mineralization and bone growth. There are two forms of natural vitamin D, vitamin D2 and vitamin D3. Natural vitamin D is obtained from 2 main sources, dietary vitamin D intake and cutaneous vitamin D synthesis from sunlight exposure. Natural vitamin D requires a 2-step enzymatic hydroxylation process to be turned into active form of 1,25-dihydroxyvitamin D, firstly, 25-hydroxylation in the liver, and secondly, 1α-hydroxylation in the kidneys. Although breast milk is highly nutritive containing adequate amounts of most important vitamins, it contains only a small amount of vitamin D, approximately 15-50 IU/L, which does not reach the recommended daily requirement of 400 IU for infants. Exclusively breastfed infants are at risk to develop vitamin D deficiency if sunlight exposure is limited. Despite the excess of sunshine for the whole year in Southeast Asian countries including Thailand, various studies have found that more than 30.0% of children and adolescents had vitamin D insufficiency. The factors associated with vitamin D insufficiency in children include maternal vitamin D deficiency, exclusively breastfed as infants, insufficient daytime outdoor activities, use of sunscreens, extensive skin coverage by clothing, and lack of vitamin D supplementation and dietary fortification. To prevent vitamin D deficiency in infants, a global consensus in 2016 recommended that vitamin D supplementation should be included in routine national health care programs along with other essential micronutrients and immunizations.