Vitamin D3 is unusual among vitamins. It's not really a vitamin, but a hormone synthesized by the body. When UVB light hits the skin, it converts 7-dihydrocholecalciferol into cholecalciferol, which is transformed into bioactive vitamin D3 in the liver and kidneys. However, in winter when light levels are low, or when dietary vitamin D3 is insufficient, high-potency vitamin D3 supplements may help.
In dietary supplements, vitamin D3 is in the bioactive form. High-potency vitamin D3 is available in liquid, tablets, or capsules in varying strengths. Infants under 1 year old require 400 IU of vitamin D every day. For ages 1 to 70, the RDA for vitamin D3 is 600 IU. The Tolerable Upper Limit -- the maximum amount of a nutrient considered safe for healthy people -- for vitamin D is 2,000 units/day.
Vitamin D3 accelerates calcium absorption from the intestines by stimulating the expression of calbindin -- a protein carrier -- and causing immediate opening of calcium channels and calcium transport into cells.
Vitamin D3 regulates the activities of osteoblasts and osteoclasts. Osteoblasts build bones; osteoclasts break down bone matrix to release calcium into the bloodstream when needed. Vitamin D3 also maintains proper blood balance between calcium and phosphorus, and helps stimulate osteoclast cell differentiation -- a process by which immature, undefined cells develop into specific cells.
Vitamin D3 deficiency is associated with muscle weakness and increased risk of falling, fractures and loss of independence in the elderly. In a review published in a 2002 issue of "The American Journal of Clinical Nutrition," researchers found severe muscle weakness, due to prolonged vitamin D-deficiency, quickly reversed with vitamin D3 supplementation.
A review published in a 2002 issue of "Osteoporosis International" posited that vitamin D3 enhances muscle strength and function by binding to nuclear receptors which result in gene transcription and subsequent protein synthesis. The researchers recommended 800 IU of cholecalciferol with elemental calcium for vitamin D- and calcium-deficient elderly people as a means of reducing fractures.
Expose your face, arms and hands to the sun for about 10 to 15 minutes a few times a week. Those with dark skin may need longer exposure. The best wavelengths for vitamin D synthesis are UVB rays between 290 and 310 nanometers. UVA rays can damage the skin.
Consume fatty fish such as salmon, sardines and herring; egg yolks; liver; beef; veal; vitamin D-fortified foods such as milk, margarine, butter and orange juice.
Vitamin D3 is safe if taken in recommended dosages. Check with your doctor before taking high-potency vitamin D3.
- Vivo.Colostate.edu: Vitamin D (Calcitriol); Arthur R. Bowen; April 2010
- "Seminars in Nephrology"; Renal and Intestinal Calcium Transport: Roles of Vitamin D and Vitamin D-dependent Calcium-binding Proteins; Johnson, J.A. & Kumar, R.; March 1994
- "Journal of Steroid Biochemical and Molecular Biology"; The Effects of Vitamin D3 on Skeletal Muscle Function and Cellular Signaling; A.J. Dirks-Naylor & S. Lennon-Edwards; March 2011
- "Arquivos Brasileiros de Endocrinologia e Metaboloigia"; Role of Vitamin D in the Neuro-Muscular Function: M.A. Pedrosa & M.L. Castro; Aug. 2005
- "American Journal of Clinical Nutrition"; Vitamin D-deficiency, Muscle Function, and Falls in Elderly People; H. Janssen, et al.; 2002
- "Osteoporosis International"; Vitamin D and Muscle Function; M. Pfeifer, et al.; March 2002
- Jupiterimages/Pixland/Getty Images
This article reflects the views of the writer and does not necessarily reflect the views of Jillian Michaels or JillianMichaels.com.