Vitamin D is a fat-soluble vitamin that is essential for normal bone growth and remodeling by maintaining adequate serum calcium and phosphate concentrations for normal bone mineralization. Vitamin D also plays a role in the reduction of inflammation, cell growth, immune function, and glucose metabolism.
Only a few foods naturally contain vitamin D (e.g. fatty fish) and most of the vitamin D from food sources is through the consumption of fortified foods (e.g. milk and cereals). Vitamin D is also produced endogenously when ultraviolet rays from sunlight trigger vitamin D synthesis.
Vitamin D deficiency is very common, particularly in the elderly, obese people, people with limited sun exposure, darker skinned individuals, and people with conditions that limit fat absorption (e.g. celiac disease, Crohn’s disease). Vitamin D deficiency affects the immune system, resulting in frequent illnesses and tiredness, and the skeletal system, causing bone and joint pain. Longterm vitamin D deficiency, particularly in children, can result in skeletal and dental issues and developmental delays.