Vitamin D is crucial for aiding the absorption of calcium and phosphorus in the intestines. Typically, with regular exposure to sunlight, dietary supplements aren't necessary since sunlight stimulates sufficient production of vitamin D in the skin. A deficiency in vitamin D can result in bone deformities in children, known as rickets, and bone weakening in adults.Vitamin D is obtained from dietary sources such as eggs, fish, and dairy, and is also synthesized by the skin. The production of active vitamin D in the skin is reliant on sunlight exposure. People who are active and reside in sunny areas generally produce most of their required vitamin D through their skin. However, in regions with less sunlight, particularly during winter months, the skin’s production of vitamin D significantly decreases, affecting the elderly and those who stay indoors. For these groups, vitamin D supplements become essential.Among the elderly in the United States, vitamin D deficiency is fairly widespread. A study highlighted that 57% of patients in a general medical ward had a deficiency, and approximately 50% of older women consume significantly less vitamin D than recommended.The Food and Nutrition Board suggests an adequate daily intake of 200 IU for individuals aged 19-50, 400 IU for those aged 51-70, and 600 IU for those over 71. A standard multivitamin typically contains 400 IU of vitamin D, which can help meet these recommendations. The updated guidelines from 2010 recommend 600 IU daily for people aged 1-70, 800 IU for those over 71, and 600 IU for pregnant and breastfeeding women. They also advise that serum 25(OH)D levels of 20 ng/mL (50 nmol/L) are sufficient, while levels above 50 ng/mL (125 nmol/L) might have adverse effects.For children, the National Academy of Sciences advises that all infants, even those exclusively breastfed, should receive at least 200 IU of vitamin D daily starting within the first two months of life. This intake should continue throughout childhood and adolescence, as determining adequate sunlight exposure for individuals can be challenging.
