Vitamin D is more than just a vitamin: it is also a hormone. Research in the last few years suggests that Vitamin D -traditionally considered a “bone vitamin”- has a role in preventing infection, heart disease, diabetes mellitus, cancer, and autoimmune diseases such as multiple sclerosis and rheumatoid arthritis. In parallel with this explosion of research, there is a change in the recommendations for optimum intake of this vitamin-hormone. The following is a brief overview of this topic.
Vitamin D comes in two forms: D2 and D3. Vitamin D2 (ergocalciferol) comes from plants and yeast. It is not as effective as Vitamin D3 at raising 25(OH)D levels in the body. Vitamin D3 (cholecalciferol) comes from animal sources and is a more potent molecule.
The best food sources of Vitamin D are fatty fish, eggs, fortified milk and cereals, and fortified milk products such as cheese and yoghurt.
Sunlight: skin makes Vitamin D3 when exposed to sunlight. However, the melanin in darker skin blocks Vitamin D production, and sunscreen with an SPF 15 blocks vitamin D production by 99 percent.
How much of Vitamin D should one take daily? The latest American Academy of Pediatrics (AAP) guidelines doubled the recommended amount for kids from the previous 200 IU to 400 IU a day for all children.
Vitamin D supplementation should be given to infants who are exclusively breast fed because the Vitamin D content of human milk is low. The Lawson Wilkins Pediatric Endocrine society and the AAP now recommend supplementation with 400 IU daily of Vitamin D beginning within days of birth.
For adults, new guidelines are awaited. The Institute of Medicine recommendations from 1997, widely regarded as outdated, suggest dosing at 200 IU for under age 50, 400 IU for age 50-70, and 600 IU for over age 70 with an upper limit of 2000 IU per day. Many experts now recommend at least 800-2000 IU per day for adults. New and definitive guidelines will clarify the matter soon.
Worldwide, at least a billion people have low blood levels of Vitamin D. It is difficult for most people to get adequate amounts of Vitamin D from diet and sunlight alone. For example, 250 ml of milk contains only 100 IU of Vitamin D3. Vitamin D supplements may be necessary for more people than previously estimated. However, indiscriminate and excessive use of supplements has significant side effects, so take them only after medical approval.
(The writer is a specialist in Internal Medicine)
