What is your vitamin D level? Some day — maybe soon — having your vitamin D level measured may become as routine as having your cholesterol checked. According to some advocates of routine vitamin D testing, the results could prove to be a useful piece of medical information.
The importance of adequate vitamin D levels in the body has been recognized for decades. In 1921, scientists proved that exposure to the sun hardens bones and prevents diseases of “rubbery,” weak bones called rickets (in children) and osteomalacia (in adults). It was later discovered that it is the vitamin D produced when the skin is exposed to sun that helps the body absorb calcium and strengthen the skeleton. Around the same time, cod liver oil was found to be a potent food source of vitamin D. Popular and scientific interest in vitamin D waned, however, once these diseases became relatively uncommon, particularly in the United States, where milk and some other foods have been routinely fortified with vitamin D since the 1930’s.
Recently, however, new research on the so-called sunshine vitamin has shown that it plays a role in many more bodily systems than just the skeletal system. In fact, a deficiency of vitamin D is thought to possibly play a role in the development of numerous diseases, from cardiovascular disease to multiple sclerosis to complications of pregnancy. All of this new attention has made vitamin D a very popular supplement and the subject of renewed scientific inquiry.
Vitamin D in the body
The human body was designed to get most of its vitamin D through exposure to the ultraviolet (UVB) rays of the sun — the same rays that cause sunburn and skin damage. “Inactive” vitamin D is derived from cholesterol and “waits” in the skin tissue until the skin is exposed to sun. (Cholesterol is produced by the liver, so consuming dietary cholesterol is not necessary for vitamin D production.) UVB rays set off a chain reaction in exposed skin that continues in the liver and finishes in the kidneys, where vitamin D is activated and sent out to tissues throughout the body. Active vitamin D is one of many body hormones, chemical messengers that regulate body functions.
Vitamin D can also be found in food (or supplements) and is absorbed like a dietary fat. Both dietary and sun-derived D are stored in fat tissue. This means the body has some capacity to store the vitamin for later use.
Active vitamin D, also known as 1,25-dihydroxycholecalciferol, calcitriol, or vitamin D3, has many functions. Some of the known functions are well understood, such as how vitamin D helps the body absorb calcium and how it hardens bones and teeth. Other functions, such as how it helps regulate the immune system, are still being studied and learned about.
What is known is that almost every cell in the body has vitamin D receptors, suggesting that it must have a role in all of them. Particularly interesting in diabetes is that the insulin-producing beta cells in the pancreas not only have the ability to accept vitamin D, but also to activate it, just as the kidneys do. This fact is made more provocative when combined with many observational studies showing that vitamin D intake and/or blood levels are somehow connected to the incidence of both Type 1 and Type 2 diabetes.
Vitamin D and diabetes
Deficiency of vitamin D has been associated with both Type 1 and Type 2 diabetes and with metabolic syndrome (a combination of high blood pressure, abnormal blood cholesterol and triglyceride levels, insulin resistance, and excess abdominal fat that often precedes or goes along with Type 2 diabetes).