Some people believe that cardiovascular disease is caused by dietary cholesterol. Scientific evidence does not support this viewpoint and it is therefore a belief (like Santa Claus). While belief in a magic cholesterol fairy is enough to satisfy the curiosity of some, other may require more solid evidence for their nutritional edification. For these people the recent evidence linking low intakes of vitamin D to increased cardiovascular risk might be of interest.
What Is Vitamin D?
Vitamin D is actually a steroid hormone. Vitamin D can be created in the skin of humans via the action of ultraviolet light or consumed in the diet. This vitamin D is then converted to its active forms, 25-hydroxyvitamin D in the liver and 1,25-dihydroxyvitamin D in the kidney. These active forms of vitamin D then enter cells were they interact with the vitamin D receptors in the nucleus, and this alters gene regulation that elicits cellular changes.
Vitamin D And Calcium
One of the functions of vitamin D is to increase calcium absorption from the intestine. In this regard, vitamin D increases blood calcium levels. Deficiencies of dietary vitamin D and low levels of sunlight exposure cause reductions in vitamin D, and this reduces calcium absorption. As plasma levels of calcium fall, cellular levels of calcium rise due to a compensatory outflow of calcium from bone. This shift in calcium metabolism is called the calcium paradox disease.
The Calcium Paradox Disease
The calcium paradox disease is problematic because the high concentrations of cellular calcium cause increases in blood pressure, and may also be a causative factor in the development of insulin resistance. The metabolic syndrome is characterised by insulin resistance, particularly in the liver. High blood pressure accompanies many of the metabolic changes that are seen the metabolic syndrome, the development of which increases the risk of cardiovascular disease.
The Calcitonin Link
Calcitonin is a hormone that is release when plasma calcium levels rise. The function of calcitonin is to lower elevated blood calcium levels. However, calcitonin may also be a satiety signal, and this may explain the inverse association between calcium intake and body weight. As body weight is associated with cardiovascular disease, low intakes of calcium may increase the risk of cardiovascular disease via the calcitonin hyperphagia link.
How Much Vitamin D?
If you are exposed to sunlight of high intensity daily, you do not need dietary vitamin D. Those who live at high latitudes or cannot access intense sunlight however, must rely on dietary vitamin D for health. The problem is that the amount of vitamin D in most foods is generally low, and food with high concentrations of vitamin D are not commonly eaten. Supplements are therefore likely necessary, and up to 2000 IU per day in adults is now recommended in the absence of sunlight.