What's the Vitamin D "Buzz" About?
Published and reviewed January 2009
The Vitamin D "buzz" in the popular press and at the water cooler is warranted. Vitamin D3 may be the most important supplement in your health maintenance arsenal. Imagine a nutrient that strengthens your bones and reduces the risk of fractures. This nutrient improves your muscle strength and function, thus reducing your risk of falls as you age. Deficiency in this compound is associated with higher risk of diabetes, high blood pressure, heart disease and cancer death. Your immune system relies upon this nutrient, and infections may be more difficult to fight if it is lacking.
Then consider that the nutrient is widely available to you without a prescription. Blood levels of this nutrient are readily measured with a simple blood test. Nevertheless, thirty to sixty percent of the population is likely to have insufficient blood levels of Vitamin D.
If you think this sounds likely a major opportunity to improve your health and that of your family, you are correct. Please read on.
How Does Vitamin D Work in the Body?
The human body accumulates Vitamin D either through photosynthesis in the skin or through absorption from the intestine. Cloud cover and northern latitudes limit the opportunity for UV-B (sunlight) exposure. Exposure to such radiant energy increases risk of skin and eye damage, and so must be limited. Skin pigment in dark-skinned individuals further reduces production of Vitamin D in the skin. Photosynthesis is thus unlikely to provide an adequate supply of Vitamin D for most of us.
Vitamin D absorbed from the intestine can come from foods, but very few foods contain significant amounts. For example, a glass of fortified milk contains only about ten percent of our daily requirement. Fatty fish (tuna, sardines, mackerel) and eggs provide natural sources, but rarely enough. Any digestive disorder that limits absorption further compromises the situation, as those with disorders like celiac disease or Crohn's disease may have trouble absorbing the fat-soluble Vitamin D. It is thus not surprising that nearly half of the world's population may have insufficient Vitamin D.
How Can Vitamin D Help Prevent Disease?
The benefits of Vitamin D in promoting musculoskeletal health have been known for many years. Vitamin D is critical to efficient intestinal absorption of calcium. Adequate Vitamin D levels also minimize removal of calcium from bones to meet daily needs in other tissues. Children deficient in Vitamin D risk growth retardation, abnormal bone development and skeletal deformities. Adolescent bone density correlates directly with Vitamin D status . Several studies in the elderly demonstrate an average 26% reduction in fracture rates with Vitamin D supplementation [2,3]. Bone that lacks adequate calcium is also painful - 93% of patients admitted to one large emergency department with muscle or bone pain were found to be deficient in Vitamin D .
Some of the reduction in fractures associated with Vitamin D supplements may be attributable to improvements in muscle performance. Muscle performance speed and strength were significantly higher in a group of elderly nursing home residents receiving Vitamin D versus placebo . The Vitamin D group gained an estimated 22% reduction in falls. Thus Vitamin D is critical to musculoskeletal development, maintenance and protection throughout the life cycle.
What is the evidence for Vitamin D's role in protection against cancer? Many tissues in the body have the ability to change the building blocks of Vitamin D to its active form, and most tissues have binding sites for Vitamin D, suggesting that Vitamin D's effects are felt all over the body. In the laboratory, Vitamin D has been shown to promote normal and orderly cell growth. Vitamin D inhibits transformation of normal cells into cancer cells and suppresses growth of tumors through interruption of the cancer cell cycle in laboratory models .
The incidence of colorectal, breast and prostate cancers is higher at latitudes further from the equator, and correlates with UV-B exposure and Vitamin D blood levels [7,8]. Cancer deaths are perhaps even more strongly correlated with Vitamin D deficiency, suggesting that the suppressive effect of Vitamin D upon cancer growth in the laboratory is also helpful in the body's fight against various cancers. Two recent studies demonstrate the potential magnitude of this effect. Patients with the highest Vitamin D levels enjoyed an 18 to 40% reduction in risk for death from colorectal cancer when compared to those with the lowest levels . A more recent study showed a 50% reduction in the incidence of colon cancer when patients with high Vitamin D levels were compared to those with low levels of the vitamin . It appears that a major step in the ongoing fight against cancer could be the assurance that everyone maintains a consistently adequate tissue level of Vitamin D.
Cardiovascular health is another active area of Vitamin D research. There are Vitamin D receptors in heart muscle. Vitamin D has been found to affect the normal maturation of heart tissue, cardiac pumping efficiency, muscle tone in the walls of arteries, and the accumulation of plaque and scar tissue. In the laboratory, Vitamin D has favorable effects upon the formation and breakdown of clots, and upon the repair of arterial lining.
Vitamin D deficiency is associated with higher blood pressure, and supplementation in deficient patients has reduced blood pressure . In 3000 patients referred for coronary angiography, patients with the lowest Vitamin D levels suffered twice the rate of cardiovascular death over a 7-year period of follow-up . More recently, low levels of Vitamin D were found to be associated with a higher incidence of fatal stroke .
The immune system is clearly regulated by Vitamin D. Receptors on special white blood cells called helper T cells allow Vitamin D to suppress attack of the immune system upon ones own tissues. This may at least partially explain the association between a higher level of Vitamin D and reduced incidence of potentially autoimmune diseases such as Type 1 diabetes , multiple sclerosis [15}, inflammatory bowel disease and rheumatoid arthritis [16}. Another type of white blood cell, called a macrophage, is better able to fight infections such as tuberculosis when Vitamin D receptors are fully stimulated.
Type 2 diabetes is a rapidly increasing illness that is influenced by Vitamin D. Production of insulin in the pancreas and responsiveness of insulin receptors elsewhere in the body are directly correlated with Vitamin D levels. Obesity is strongly associated with this type of diabetes. Obese individuals absorb Vitamin D less well from their intestine. Circulating levels of Vitamin D are potentially reduced in such individuals through a leaching of this fat-soluble vitamin from the blood into fatty tissues, making it less available in other target organs.
Finally, a recent study that received considerable attention described an association between Vitamin D levels and overall mortality. The authors combined a group of trials where an average of 528 IU of Vitamin D supplement was compared to placebo. Over an average follow-up of nearly six years, overall mortality was reduced in the Vitamin D group by 7 percent .
How Much Vitamin D Do We Need?
Vitamin D arriving in the bloodstream from the skin or from the intestine is not yet biologically active. The liver first converts it to 25-hydroxy Vitamin D (25OHD), which is the form measured in the standard Vitamin D blood test. 25OHD then travels to the kidneys and other target tissues where it is finally converted to its active form. How much 25OHD is enough to assure health benefits? It appears that a blood level of at least 30 ng/mL is necessary for optimal musculoskeletal benefits. Levels required for maximum cancer and cardiovascular benefits may be higher, with some studies suggesting 40 to 50 ng/mL as a target to achieve those latter benefits. Vitamin D insufficiency has been defined as a 25OHD level between 20 and 30 ng/mL. Deficiency is typically defined as a 25OHD level less than 20 ng/mL.
Vitamin D supplements are typically available as either cholecalciferol (D3) or ergocalciferol (D2). It appears that D3 is about three times as effective as D2 at raising measured 25OHD blood levels to the above targets. Standard published nutritional guidelines suggest daily D3 intake of 200 IU daily in children and adults up to age 50. The American Academy of Pediatrics, recognizing the increasing evidence of Vitamin D benefits, recently increased their guideline to 400 IU daily for children. 600 IU daily has been the standard guideline for people over 70 years old. None of these targets may be high enough! It appears to require an intake of 800 to 1000 IU of Vitamin D3 daily to maintain a blood 25OHD level of 30+ ng/mL. Even that amount may be inadequate in some elderly people confined indoors. Look for new guidelines in the months to come.
In the meantime, what should be done? It might be ideal to measure blood 25OHD levels in every individual, and then add D3 supplementation to achieve a blood level of 30 to 40 ng/mL. However, given the cost of 25OHD blood tests and the need for containment of health care costs, it would seem a reasonable compromise to measure levels only in those with osteoporosis/fractures and those at highest risk for deficiency - homebound, elderly, living in northern latitudes, obese, or suffering from malabsorptive or kidney diseases. The rest of the population should be able to achieve the desired blood level by simply being sure to get 800 to 1000 IU of daily D3 intake. Doses of 2000 IU daily have been proven to be consistently safe, and much higher doses appear to be safe over several months to restore levels in deficient patients.
Listen to the Vitamin D "buzz" and discuss it with your family and friends. Are you getting enough of this critical vitamin? Do the math, looking at your diet and your supplements and reading labels carefully. Speak with your primary care physician. Your body will thank you many times over!
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14. Harris SS. Vitamin D in type 1 diabetes prevention. J Nutr. 2005;135:323-325.
15. Munger KL, Levin LI, Hollis BW, et al. Serum 25-hydroxy vitamin D levels and risk of multiple sclerosis. JAMA. 2006;296:2832-2838.
16. Merlino LA, Curtis J, Mikuls TR, et al. Vitamin D intake is inversely associated with rheumatoid arthritis: results from the Iowa Women's Health Study. Arthritis Rheum. 2004;50:72-77.
James L. Budd, M.D.
James L. Budd, M.D. is an internal medicine specialist practicing with Twelve Corners Internal Medicine in Brighton. He is also an Assistant Clinical Professor of Medicine at the University of Rochester School of Medicine.
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