Vitamin D Dietary Intake through Dairy Products to Reduce the Risk of Osteoporosis

Abstract

Background: Vitamin D and calcium are important dietary compounds that affect bone mass, even if other minerals (potassium, zinc, etc.) and other vitamins (A, C and K) are also involved. Vitamin D and other minerals, in fact, play an important role in calcium homeostasis and calcium absorption. Hip fractures incidence is higher in western countries, where calcium is frequently included in human diet, while the occurrence of these fractures is lower in developing countries, where diets are often poor in calcium. This situation is known as the “calcium paradox”, and may be partially explained considering phosphate toxicity, that can induce a disorder of mineral metabolism. It is important to maintain adequate dietary calcium-phosphate balance in order to perform a healthy life, reducing the risk of osteoporotic fracture in older people. Vitamin D can also act as a hormone; vitamin D2 (ergocalciferol) is derived from the UV-B radiation of ergosterol, the vitamin D precursor naturally found in plants, fungi, and invertebrates. Vitamin D3 (cholecalciferol) is originated by sunlight exposure from 7-dehydrocholesterol, a precursor of cholesterol that can also act as a provitamin D3. Dietary intake of vitamin D3 is very important when skin is exposed for short times to ultraviolet B light (UV-B) one of the three kinds of invisible light rays together with UV-A and UV-C. This can be considered the usual situation in northern latitudes and in winter season, or the typical condition for older people and/or for people with very white delicate skin. Actually, the recommended daily intake of dietary vitamin D is strictly correlated with age, ranging from 5 μg for infants, children, teen-agers and adults, including women during pregnancy and lactation, to 15 μg for people over 65 years.