Vitamin D, Steroid King of the Vitamins

Vitamin D has long been known for its role in preventing rickets in children and as a required element for the intestinal absorption of dietary calcium. We are now finding vitamin D to be important in protecting the body from a number of diseases. Vitamin D deficiency has been linked with stroke, cardiovascular disease, osteoporosis, osteomalacia, several types of cancer, some autoimmune diseases such as multiple sclerosis, rheumatoid arthritis, and types 1 and 2 diabetes, depression and schizophrenia.

Vitamin D has a chemical structure very similar to some of the most important hormones in the human body; and, in many ways, behaves very much like a hormone, a steroid hormone. It binds to specific vitamin D receptors (like a lock and key) in target tissues and turns on specific genes. We know it has profound effects on immunity seen as antiviral and antibacterial effects. It maintains muscle and bone health to such a degree that, in one study, nursing home residents who were given vitamin D supplements had fewer falls than their supplement-free fellow residents. Those on the vitamin D supplementation had fewer fractures when they did fall, compared to the supplement-less residents. No other interventions were performed; just the addition of vitamin D supplements.

Humans begin the process of making vitamin D in their skin when it is exposed to sunlight. Ultraviolet light acts on a cholesterol based molecule in the skin to produce vitamin D3, which is technically a prohormone or precursor to a hormone. Our skin is capable of producing 30,000 units of vitamin D per day. Granted, this would require us to live like cave people, that is, nearly naked and outdoors all day. There is reduced endogenous vitamin D production at times of the year with reduced ultraviolet light (winter), and that is the reason that winter is the season for colds and flu. Also, due to concerns about sun damage and skin cancer, many Americans have limited sun exposure all year. (Let's face it, when we lived as cave people we didn't live long enough to get skin cancer; and we had an intact ozone layer.) The vitamin D produced in the skin is then hydroxylated in the liver to form the 25-hydroxy metabolite that is the main circulating form of the prohormone (still a prohormone). 25-hydroxy vitamin D has a long half-life (hangs around a long time) and is stored in the adipose or fatty tissue. This metabolite is ultimately transformed in the kidneys to form 1, 25-dihydroxy vitamin D--at last, the active form of the hormone.

Formation of active vitamin D is regulated by the parathyroid glands, 4 small glands located near the thyroid glands. When there is a vitamin D deficiency the parathyroid glands work overtime to stimulate the kidneys to produce more of the active form of vitamin D. For this reason, levels of active vitamin D can appear normal, or even elevated, in the presence of a deficient state. In order to truly measure vitamin D status the precursor to the active form of vitamin D is measured to determine the total bioavailability of vitamin D.

Many vitamin D supplements are actually vitamin D2, which is not found in animals. Ergosterol, a compound in fungal cell membranes, is exposed to ultraviolet light to manufacture vitamin D2 commercially. Vitamin D2 is metabolized and activated in the body much like vitamin D3, but it acts for a shorter time and is less active in the body than vitamin D3. Vitamin D2 has to be given in larger doses and more frequently to maintain adequate levels of vitamin D. Given enough vitamin D2, the body's production of vitamin D3 is decreased (suppressed). If vitamin D3 (what humans make) is measured in a person who is taking vitamin D2 (what fungi make), levels can appear low, as if there is a vitamin D deficiency. The take home message is that if you are taking vitamin D2, then you need to measure vitamin D2 levels when you are checking vitamin D levels.

Who Is At Risk For Vitamin D Deficiency?

Elderly people are at risk for vitamin D deficiency for several reasons. As we age, we make less vitamin D precursor in the skin, and our parathyroid glands do not function as well as they once did. Vitamin D deficiency is associated with osteoporosis and muscle weakness, as well as muscle and joint pain.

Dark-skinned people (including children) are at risk for vitamin D deficiency because they require much longer exposure to ultraviolet light in order to create enough circulating vitamin D compared to more fair-skinned individuals.

People who live at latitudes far from the equator (greater than 35 degrees latitude) or those who have limited sunlight exposure due to their work environment or their cultural rules of dress are at risk for low vitamin D levels.

Anyone with musculoskeletal pain (pain in the muscles, joints, or bones) should be tested for vitamin D deficiency because patients with diagnoses of fibromyalgia, low back pain, non-specific musculoskeletal pain, and hypothyroidism are often found to have low vitamin D levels. Supplementation improves symptoms.

All children need adequate vitamin D levels to prevent rickets and allow normal bone development. Infants who are breast-fed, especially those breast-fed by vitamin D deficient mothers, may not be getting enough vitamin D. Maternal supplementation is one solution. Cod liver oil is one of the few foods that provide a good amount of vitamin D and is a great supplement for infants and children. (Your grandmother was right!) Vitamin D deficiency in infants and children is associated with the development of childhood type 1 diabetes.

Overweight or obese people have lower levels of circulating vitamin D because their vitamin D can be bound up in fat stores.

Why Measure Vitamin D?

Vitamin D deficiency can be completely asymptomatic (at least for awhile), and so is often detected as part of routine testing. Deficiency is simple to detect. Supplements are inexpensive and easy to obtain and can improve health status and prevent more serious diseases.

What Is a Healthy Level of Vitamin D?

Levels under 32 ng/ml have traditionally been thought to indicate vitamin D deficiency; and, by anyone's standards, do represent vitamin D deficiency. This accepted standard was originally developed in relation to prevention of rickets. As it turns out, a minimal amount of vitamin D will prevent rickets; and many experts now agree that levels should be higher than 50 ng/ml (and probably 75 ng/ml) for optimal health. Research is in progress to establish more definitive requirements.

Who Needs Supplements, And What Type Is Best?

It is likely that most Americans are vitamin D deficient and need supplementation unless they are already taking it. A simple blood test will detect deficiency, and supplements are widely available. Vitamin D3 is the same as our own natural vitamin D and is more bioactive than vitamin D2 with less risk for toxicity. Supplements that contain probiotics are better absorbed and are good for the digestive system. There is good evidence that daily supplementation of 1000 to 5000 u of vitamin D3 is optimum.

For more information contact Lisa Hogan, MD at Youthology, Aesthetic & Anti-Aging Medicine at 919-847-1495 or lisa@youthology.md or visit www.youthology.md.