Vitamin C (ascorbic acid) functions as an antioxidant, much like p-carotene. It is also involved in the synthesis of collagen in the skin and other connective tissues. It promotes resistance to infection through its involvement with the immune activity of leukocytes, inflammatory reaction processes, and mucous membrane integrity. Megadoses of vitamin C are often promoted as a means to prevent and treat the common cold; however, the evidence provides only weak support for this claim . Vitamin C deficiency results in scurvy.
Vitamin D is essential in bone health by regulating calcium and phosphorus. Because the body can make vitamin D with the help of sunlight, people can meet their requirement via sun exposure, as well as from the diet. Direct sun exposure to the skin for 30-60 min weekly is sufficient to maintain vitamin D status for most white people. However, people with dark-colored skin and older adults synthesize less vitamin D from sun exposure. Individuals who apply sunscreen with an SPF factor of 10 can reduce vitamin D production by 90%. Those who reside at latitudes around 40° north or south have insufficient UVB radiation available for at least 5 months of the year. For these people, a diet containing ample amounts of vitamin D-rich foods or supplements is particularly important. Vitamin D also exhibits many non-skeletal effects, particularly on the immune, endocrine, and cardiovascular systems [11, 12].
Vitamin D deficiency depresses calcium absorption which can lead to abnormal bone development. Children who fail to obtain enough vitamin D can develop the deficiency disease rickets (leg bowing); in adults, it is called osteomalacia. Long-term vitamin D insufficiency may also contribute to osteoporosis. Excess vitamin D induces abnormally high serum calcium levels and deposition in soft tissues resulting in bone loss, kidney stones, and calcification of organs such as the heart and kidneys.