Much like vitamin A, vitamin D is another fat soluble vitamin. In fact, it is not even really a vitamin, it is technically a hormone. As I'm sure most know, it is present in sunlight and our bodies absorb it from the sun into our skin. Our bodies have vitamin D receptors in our bones, pancreas, intestine, kidneys, brain, spinal cord, male and female reproductive organs, thymus, adrenal glands, pituitary, and thyroid gland.
There are two types of vitamin D - D2 (ergocalciferol) and D3 (cholecalciferol). D2 can be found in plants and D3 comes from red meat and fish.
Functions of vitamin D in your body:
- Aids in the absorption of calcium from the intestinal tract
- Helps the body assimilate phosphorus
- Stimulates bone cell mineralization
- Helps the pancreas release insulin (1,2,3)
Things that decrease vitamin D in your body:
- Aging (your body makes less vitamin D from the sun)
- Meds (e.g., phenytoin - anti-convulsive medication)
- Decreased fat absorption
- Sunscreen (prevents vitamin D absorption)
- Prednisone (interferes with the conversion of vitamin D
to its active form) (4,5,6)
Top 10 food sources:
6. Sunflower seeds
10. Natural cheeses (6)
There you have it - vitamin D in a nutshell. Next up - vitamin E!!!
1. Holick, M., et al., "Vitamin D and bone health," J. Nutr 1996; 126: 1159S-1164S.
2. Dawson-Hughes, B., et al., "Effect of vitamin D supplementation on wintertime and overall bone loss in healthy postmenopausal women," Ann Intern Med 1991; 115 (7): 505-12.
3. Dawson-Hughes, B., et al., "Effect of calcium and vitamin D supplementation on bone density in men and women 65 years of age or older," NEJM 1997; 337 (10): 670-76.
4. Collins, J., What's Your Menopause Type? Roseville, California: Prima Publishing, 2000, p. 207.
5. Ibid., Bland, Clinical Nutrition: A Functional Approach, p. 133.
6. Ibid., Bland, Clinical Nutrition: A Functional Approach, p. 133.