Vitamin D

Vitamin D is a fat-soluble vitamin, which means that after it is ingested, the body makes use of what it needs and keeps any remainder in fat storage for the future.  For this reason, healthy individuals do not need daily doses of fat-soluble vitamins (although relative regularity is important) for healthy functioning.  By contrast, individuals who are not able to store or digest these vitamins due to conditions like cystic fibrosis may need to ensure that they are getting enough Vitamin D on a daily basis.

The Role of Vitamin D in the Body

Vitamin D helps the body absorb calcium and maintain appropriate levels of phosphorous and calcium in the blood; it is also important for bone remodeling and bone growth. Getting enough of this vitamin is crucial for the prevention of osteomalacia (bone softening) in adults and rickets (soft bones and abnormal bone growth) in children. By increasing the density of mineral in bone, Vitamin D can help reduce the risk of bone fractures.  Another of its roles is promoting immune function and reducing inflammation.  Vitamin D is believed to play a role in the prevention of breast, colon, and prostate cancers; it may also be beneficial in preventing and treating conditions like type 1 and type 2 diabetes, multiple sclerosis, and high blood pressure.

Sources of Vitamin D

Exposure to the sun is one of the most common sources of Vitamin D.  Even people who live in regions with cloud cover and lack of sunshine during the autumn and winter months are likely to obtain sufficient supplies of Vitamin D during spring and summer months that can be stored and used later.  Although sun exposure through glass (e.g., a window at home or work, or the car windows or windshield) will not give you any Vitamin D, there is some evidence to suggest that the skin can still synthesize it even if the person is wearing sunscreen.  The amount you can obtain from prolonged sun exposure is limited and, obtaining Vitamin D should not be a priority over protecting your skin from sun damage including the possibility of cancer.  Natural food sources of Vitamin D are relatively limited compared to those of most other vitamins; flesh from fish like tuna, salmon, and mackerel as well as certain fish oils are the most abundant sources. Cheese, egg yolk, and beef liver contain small amounts.  Some common grocery items have been fortified with Vitamin D, originally as a public health move to decrease the incidence of rickets.  These include milk, yogurt, some cereals, orange juice, and margarine.

Insufficient Vitamin D

In adults, bone pain and muscle weakness may signal a deficit but may not help in detection until later stages. Those at greatest risk for a deficiency include infants who are breastfed for extended periods without supplementation and whose mothers have insufficient Vitamin D themselves; individuals with diseases such as Crohn’s, cystic fibrosis, and liver disease (which may inhibit absorption); those who have undergone gastric bypass surgery; individuals with dark skin; seniors; and those who remain indoors or wear clothing that limits sun exposure.

Toxicity of Vitamin D

Symptoms of excessive Vitamin D include weight loss, anorexia, irregular heart rhythms, and an excessive output of urine.  High amounts also increase the chances of cardiovascular events and pancreatic cancer.