Vitamin D Gains Respect

Once regarded as just another nutrient, vitamin D is vital for good health and holds promise for the treatment of disease

Everyone knows that vitamin D builds strong bones by helping the body absorb calcium. But new research indicates that it’s essential for nearly every other part of the body, too.

Vitamin D deficiency is now recognized as a significant problem in developed countries like the United States. Clinical studies have found intriguing associations between low levels of vitamin D and diseases like diabetes, cancer, depression, hypertension, osteoporosis, muscle disorders, multiple sclerosis, arthritis and heart disease. These associations have made this essential nutrient the subject of many basic science research studies.

Robert Simpson, Ph.D., Stephen Hershey, M.D., and Dina Bauer, Ph.D., who is holding one of the lab’s spontaneous hypertensive heart failure rats Photo: Martin Vloet

“People used to think vitamin D was just one in a long list of nutrients in your morning multi-vitamin pill, but now we know how important it is, and how much promise it holds for developing future therapeutic drugs,” says Robert Simpson, Ph.D., a professor of pharmacology in the Medical School.

Simpson has spent 25 years studying the secrets of vitamin D, and he says it’s gratifying to see it finally getting the respect it deserves from the scientific community.

“Vitamin D isn’t really a vitamin at all,” Simpson says. “It’s a substance the body converts into a hormone called 1,25 dihydroxyvitamin D or calcitriol. The process begins with sunlight. When ultraviolet light from the sun hits your skin, it reacts with a steroid molecule in skin cells to create vitamin D. It’s transferred from the skin to your liver and kidneys where it is metabolized into calcitriol, the activated form of the vitamin.”

Simpson was the first scientist to identify the docking site, or receptor, calcitriol uses to affect heart muscle cells called cardiomyocytes. He and other scientists have found the same receptor on many other types of cells. When calcitriol binds to the vitamin D receptor, it sends a signal to the cell’s nucleus telling it to turn on, or turn off, certain genes. This makes calcitriol one powerful hormone, because it can alter gene activity in most cells and affect the function of many organs in the body.

Simpson believes that the ability of our cells to respond to vitamin D’s signal developed early in human evolution as a sort of internal “wake-up call” triggered by exposure to sunlight. After all, our ancestors didn’t just hang around the cave all day. They were outside hunting and gathering food, in a dangerous environment where survival could depend on every organ in the body operating at peak performance.

In 2004, Simpson received a $1.2 million grant from the National Institutes of Health to study the relationship between the vitamin D hormone and a condition called cardiac hypertrophy, or progressive heart failure, which affects nearly 5 million Americans.

Heart failure can develop when damage from a heart attack or chronic high blood pressure makes the heart work harder than it should for long periods of time. As a result, the heart gets larger, and its cells don’t contract and relax together. This makes the heart less efficient at pumping blood. Over time, cardiac muscle dies, scar tissue forms and the heart gets weaker. Although drugs can help slow the process, doctors currently have no way to stop the heart’s gradual deterioration.

“In our laboratory, we study rats and mice that either can’t make enough vitamin D hormone or lack the vitamin D receptor,” Simpson says. “These animals have abnormally large hearts and cardiac muscle cells, similar to what physicians see in people with heart failure. We think that a lack of vitamin D hormone leads to defects in the heart’s extra-cellular matrix resulting in inefficient contractions.”

In studies conducted by other researchers, patients with heart failure were found to have vitamin D levels as much as 50 percent lower than similar patients without the disease.

Ultimately, Simpson hopes his research will lead to new drugs for heart failure. He’s trying to identify genes that are active in cardiomyocytes and figure out how they are regulated by the vitamin D hormone. He’s also looking for slight genetic differences in the human gene for the vitamin D receptor to see if these differences are more common in people diagnosed with heart failure.

Because it is so vital for good health, Simpson says it’s important to make sure you get enough vitamin D. The federal government recommends adults get 400 international units of vitamin D every day. The recommended amount for adults over age 55 is 800 international units. Since only a few foods — like fortified milk, egg yolks and salmon — contain vitamin D, Simpson says it’s difficult to get an adequate supply through diet alone.

“Sunlight is the best source,” he says. “Fifteen minutes of direct exposure without sunscreen several times a week is enough to allow your skin to produce the recommended dose.”

Of course, if you are at high risk for skin cancer, you need to check with your doctor and weigh the risks and benefits of sun exposure carefully. Born and raised in sunny southern California, Simpson includes himself in this category. “I’ve had several pre-cancerous lesions removed from my face,” he says. “So I follow my dermatologist’s recommendation and use sun-blockers. But I also take vitamin D supplements every day.”

If you have dark skin, live in a northern climate where it’s cloudy much of the winter, have a history of skin cancer, or spend more time indoors than outside, taking daily vitamin D supplements can help, according to Simpson. “But too much can be toxic,” he warns. “So don’t take more than the recommended dose without consulting your physician.”

—SFP

For more information on sources and recommended amounts of vitamin D:
http://ods.od.nih.gov/factsheets/vitamind.asp