Everyone needs strong bones. Vitamin D promotes calcium absorption in the gut and maintains adequate serum calcium and phosphate concentrations to enable normal mineralization of bone. It is also needed for bone growth and bone remodeling by osteoblasts (bone growth cells) and osteoclasts (bone destruction cells). Without sufficient vitamin D, bones can become thin, brittle, or misshapen. Vitamin D sufficiency prevents rickets in children and osteomalacia in adults. Together with calcium, vitamin D also helps protect older adults from osteoporosis.
Everyone needs a strong immunity. Vitamin D has the roles in immune function, and reduction of inflammation. Clinical studies suggest that vitamin D enhances anti-mycobacterial immunity, and that deficiency is associated with susceptibility to active disease. High doses of vitamin D were widely used to treat active tuberculosis in the pre-antibiotic era. Recently, a number of clinical studies have demonstrated that a vegetarian diet (low in vitamin D) is an independent risk factor for active tuberculosis.
Everyone needs cell replacement. Many genes encoding proteins that regulate cell proliferation, differentiation, and apoptosis (programmed death) are modulated in part by vitamin D. Many cells have vitamin D receptors, and some convert 25(OH)D to 1,25(OH)2D. Millions of you cells die and regenerate every day. You need enough vitamin D to stay healthy.
Vitamin D is a fat-soluble vitamin that is naturally present in very few foods, added to others, and available as a dietary supplement. It is also produced in the body when ultraviolet rays from sunlight strike the skin and trigger vitamin D synthesis. If your diet and sunlight cannot provide you enough vitamin D, you need to take vitamin D supplement.