Scientists and nutritionists classify vitamin D as a fat-soluble vitamin, which means that it requires the presence of fat cells for absorption and that the body can store vitamin D in fat and liver cells. Although officially classified as a vitamin, the active form of vitamin D is actually a steroid hormone similar to other steroid hormones such as estrogen. Vitamin D does not contain estrogen, but the two hormones may affect one another and they both play a vital role in maintaining healthy bones.
Estrogen
The term "estrogen" describes a group of hormones including estrone, estradiol and estriol. Although estrogen hormones occur in men and women, this article will discuss estrogen in relation to the woman's body because the interaction with vitamin D and role in bone strength is more pronounced in women than men. The role of estrogen hormones, as with any hormone, is to carry information or instructions from one group of cells to another. In women, the majority of estrogen hormones are produced in the ovaries, adrenal glands and fat tissues. Estrogen hormones bind to estrogen receptors found in the breast, uterus, brain, bone, liver and heart.
Vitamin D
Your body gets vitamin D from two sources: the food you eat and the sun. Very few foods naturally contain a form of vitamin D called vitamin D3, but they include beef liver, egg yolks and fatty fish such as tuna and salmon. Food manufacturers fortify other foods such as milk, orange juice and breakfast cereals with vitamin D. Your body produces the majority of its vitamin D by exposure to the ultraviolet rays from the sun. When triggered by the sun, your skin cells convert a substance known as 7-dehydrocholesterol into previtamin D3, which then becomes vitamin D3. All of these forms of vitamin D remain biologically inactive until an enzyme in the liver, known as 25-hydroxylase, converts vitamin D3 into 25-hydroxycholecalciferol and then 1-alpha-hydroxylase in the kidneys transforms it into the biologically active vitamin D known as 1,25-dihydroxycholecalciferol.
Effects on Bones
Your body continually breaks down old bone tissue and produces new bone material, which requires calcium -- a mineral that adds strength to bone. Your body cannot efficiently absorb calcium without vitamin D. This makes vitamin D vital for bone growth and development. Vitamin D also stimulates the absorption of phosphate and magnesium, which also help build strong bones. When a women enters the phase of life known as menopause, her body stops producing eggs and the production of estrogen falls dramatically. The drop in estrogen levels increases the rate of bone loss and can lead to a condition known as osteoporosis, a condition of thin, weak bones. The interaction between estrogen and vitamin D may contribute to this effect.
Interactions
The presence of estrogen may affect the production of the biologically active form of vitamin D, according to research published in the "The Journal of Clinical Endocrinology and Metabolism." In this study doctors treated a group of women with osteoporosis with estrogen. The group who received the estrogen treatment experienced an increase in calcium absorption. When testing the amount of biologically active vitamin D in the blood, the study found an increase that correlated with the increase in calcium absorption. The scientists concluded that estrogen may increase the production of active vitamin D by stimulating the enzyme 1-alpha-hydroxylase in the kidneys.
References
- Linus Pauling Institute; Vitamin D; Victoria Drake; January 2008
- Colorado State University; Vitamin D; R. Bowe.; April 2010
- "The Journal of Clinical Endocrinology and Metabolism"; Effect of Estroen on Calcium Absorption and Serum Vitamin D Metabolites; J. Gallagher, et al.; December 1980
- "Endocrinology"; Vitamin D Is an Important Factor in Estrogen Biosynthesis of Both Female and Male Gonads; K. Kinuta, et al.; April 2000
- National Institutes of Health Office of Dietary Supplements; Vitamin D; February 2011
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