What is the function of vitamin D?
The hormonal functions of vitamin D include regulation of bone health, regulation of muscle health (including both skeletal and heart muscle), regulation of immune response, regulation of insulin and blood sugar, and regulation of calcium and phosphorus metabolism. Further details about these functions are presented in the paragraphs below.
What events can indicate a need for more foods rich in vitamin D?
Muscle aches and muscle weakness
Frequent falls, particularly among older persons
Bone pain, frequent bone fractures, or soft bones
Stunted growth in children
Asthma in children (especially severe asthma)
Impaired cognitive function, especially among older persons
Chronic low energy and fatigue
Depression, particularly among older persons
Presence of any autoimmune disorder
Lack of exposure to sunlight for any reason, including geography, use of sunscreen, or wearing of protective clothing
Concentrated food sources of vitamin D include salmon, sardines, shrimp, milk, cod, and eggs. Among salmon, wild-caught fish have been shown to average significantly more vitamin D than non-organically farmed fish.
Since cow's milk-containing foods are an important source of vitamin D in the United States, and since most dairy products are not only fortified with vitamin D but also pasteurized prior to retail sale, there is good research data on the stability of vitamin D under different heating and storage conditions. Researchers have found virtually no loss of vitamin D following pasteurization of processed cheese under normal commercial conditions. They have also found a vitamin D loss of about 25-30% when cheese is exposed to an oven temperature of 450°F (232°C) for approximately 5 minutes. Since foods like frozen cheese pizzas are often cooked in the oven at temperatures between 400-450°F (204-232°C) for approximately 20 minutes, this research tells us that we can expect at least one-fourth of the vitamin D to be lost during the pizza re-heating process. This percentage of vitamin loss is still relatively low, however, in comparison to similar heating of other foods and loss of other vitamins (especially less heat-stable vitamins, like vitamin C).
Storage of cheese over a 9-month period at temperatures ranging from 39-84°F (4-29°C) have shown virtually no loss of vitamin D, also underscoring the relative stability of this vitamin.
It would be very difficult to overestimate the importance of recent discoveries about vitamin D and the immune system. Vitamin D's role in immune regulation has revolutionized research in this area to such a degree that it is virtually impossible to investigate an autoimmune disease without considering the possible role of vitamin D. This statement holds true for health conditions like rheumatoid arthritis, multiple sclerosis, Crohn's disease, systemic lupus erythematosus, and numerous other autoimmune conditions.
Prevention of cancer
The role of vitamin D in cancer prevention is a lively area of current research, and the mechanisms linking vitamin D to cancer prevention are not completely evident. Nevertheless, research has shown a clear role for vitamin D in prevention of the following types of cancer: bladder cancer, breast cancer, colon cancer, ovarian cancer, prostate, and rectal cancer. In certain situations, vitamin D may also play a role in cancer treatment. Vitamin D analogs (vitamin-D like substances synthesized in the laboratory) are actively being tests as anticancer agents, especially with respect to breast and prostate cancers.
What are deficiency symptoms for vitamin D?
Bone pain, frequent bone fractures, and softening of the bones can all be symptoms of vitamin D deficiency. So can muscle aches and muscle weakness since vitamin D helps to regulate muscle composition and prevent too much fat accumulation alongside of muscle tissue. In this context, especially in older persons, frequent falls can point to deficiency of this vitamin. The key role of vitamin D in regulation of immune response means that lowered immunity can be a symptom of vitamin D deficiency, as can the presence of any autoimmune disorder. In older persons, cognitive problems (disturbances in thought processes) and depression can be symptomatic of vitamin D deficiency, and in children, stunted growth and severe asthma have also been shown to have vitamin D deficiency as potential causes.
What are toxicity symptoms for vitamin D?
Excessive intake of vitamin D can be toxic, and toxicity of vitamin D can come from either its plant-based (D2) or animal-based (D3) form. Symptoms of toxicity include loss of appetite, nausea, vomiting, high blood pressure, kidney malfunction, and failure to thrive. However, it is also important to note that vitamin D deficiency poses a far greater risk to the vast majority of individuals than vitamin D toxicity and that vitamin D toxicity from food intake is extremely unlikely. Less than one-third of all persons in the U.S. meet the Dietary Reference Intake level for vitamin D, and are far from consuming anything close to potentially toxic levels.