Vitamin D Basics

Bob McCullen, MD
 
Vitamin D promotes calcium absorption in the gut and maintains adequate serum calcium and phosphate concentrations to enable normal mineralization of bone and to prevent low calcium muscle contractions called tetany. It is also needed for bone growth. Vitamin D helps prevent osteoporosis in adults and rickets/osteomalacia in children. Also it is important in many cellular functions including cell growth, neuromuscular and immune functions, and cell differentiation. Vitamin D is formed in the skin due to sunlight exposure, is found in a very few foods, and in supplements. All these forms of Vitamin D are inactive and must go through the liver and kidney to get to the active state.  There is considerable controversy on what serum level constitutes a deficiency of Vitamin D. Part of the problem is the difficulty in measuring the active Vitamin D in the blood. Therefore it is often easier to discuss the Recommended Daily Allowance for Vitamin D.
 
They are:
1-12 months – 400 IU per day
1-70 years – 600 IU per day
Above 70 – 800 IU per day
 
Unfortunately only a small number of foods have Vitamin D in them. Examples are fatty fish (salmon, tuna, mackerel), fish liver oils. Smaller amounts of Vitamin D are found in beef liver, cheese, and egg yolks. Also many foods are supplemented with Vitamin D such as milk, cheese, yogurt, and breakfast cereals.
 
There are groups of people who are at greater risk for Vitamin D Deficiency than others. Those include breast-fed infants, older adults, darker skin, people with little sun exposure, those with inflammatory bowel disease or malabsorption issues and those who have undergone gastric bypass. Other beneficial effects of Vitamin D are less well understood, but include decrease cancer risk, prevention and treatment of type 1 and type 2 diabetes, hypertension, glucose intolerance, multiple sclerosis, and other medical conditions.
 
So eat your fish or add a Vitamin D supplement as shown above. Do not overdo your vitamin supplements. You do not get any extra beneficial effects from super high levels and toxicity can occur with these high levels