[Hypovitaminosis D: a major worldwide public health problem]

PHYSIOLOGY: Vitamin D increases intestinal absorption of calcium favoring the microenvironment necessary for bone mineralization. In addition, vitamin D prevents hypocalcemia via its osteoclastic action. Severe hypovitaminosis leads to rickets in children and its equivalent in adults, osteomalacia. Mild to moderate hypovitaminosis D causes secondary hyperparathyroidism increasing the risk of fracture, particularly femoral neck fracture. Vitamin D would also have an antiinflammatory and anticancer effect.

Hypovitaminosis D is frequently observed in Europe in the elderly, particularly in the institutionalized population, but is also seen in otherwise healthy younger adults. An estimated 40% of the young European population has some degree of hypovitaminosis D. Surprisingly, it is more frequent in sunny Mediterranean countries than in certain northern countries such as Norway. The lower incidence observed in the United States is probably related to the vitamin D supplementation of the American diet. Hypovitaminosis D in Africa and the Middle-East is also an important problem, being considered to be one of the 5 most prevalent childhood diseases in developing countries.

The limited quantity of vitamin D in food and multiple environmental factors contribute to hypovitaminosis D. These factors include insufficient sun exposure and urban lifestyle with a high degree of pollution. In addition, cutaneous photosynthesis of vitamin D is limited by hyperpigmentation in black people, wearing traditional veils that limit sun exposure, and use of sun lotions, further contributing to vitamin D deficiency.

The very high prevalence of hypovitaminosis D in the world, and particularly in Europe, Africa and the Middle-East, points to the need for public health measures in these countries. While waiting for these measures to be implemented, vitamin D supplementation (for example in tablet form) should be encouraged in order to meet minimum requirements. Finally, the beneficial effect of moderate sun exposure on cutaneous vitamin D synthesis (and psychological well-being) must not be overlooked.