Calcium, vitamin D, and selenium. The extent of calcium, vitamin D, and selenium deficiency in developing countries is uncertain. Calcium consumption is extremely low in many locations where dairy products and fish are not eaten, but humans have the capacity to absorb calcium more efficiently in these situations. Very low calcium consumption does not seem to impair children's growth, but may reduce their bone mineralization. Low dietary calcium may be the explanation for non-vitamin D rickets in Nigeria, South Africa, and several other countries.
Calcium deficiency is certainly a risk factor for osteoporosis in later life.
Vitamin D deficiency, which is caused primarily by low exposure to ultraviolet light, is common in more northern and southern latitudes and in regions where infants and women are heavily clothed for cultural or religious reasons. In Europe and China, where few foods are fortified with vitamin D, infants born at the end of winter commonly show evidence of vitamin D deficiency. Selenium deficiency is localized in specific but large geographic regions, including China and parts of Africa, where it can exacerbate the symptoms of iodine deficiency and interfere with the anti-goiter benefits of iodine supplements. Focusing on the elimination or reduction of iodine, vitamin A, and iron deficiencies has motivated many agencies and governments to work together and has demonstrated the benefits of intervention programs. Clearly, efforts are also needed to assess the prevalence of other micronutrient deficiencies.