Although vitamin D is just one of many factors that powerfully affect your health, it is one that has until very recently been largely overlooked by doctors and their patients and by many folks who are otherwise quite health conscious. 

Vitamin D is unique in that you get very little from food.  The best and only natural source is exposure to the ultraviolet rays of the sun, which stimulate vitamin D production in your skin.  Most people, even in sunny southern California, don’t get enough sun exposure to make optimal amounts of D, and due to staying indoors too much, wearing lots of clothes, and using sunscreen to protect the skin, many people are deficient.  There is a blood test for vitamin D levels, called 25D-hydroxy (25D for short).  Very frequently adults as well as children are deficient.  There have been studies indicating that Vitamin D levels in pregnant and nursing women and in newborn babies are often very low.  There is evidence that low D levels in the first years of life significantly increase the chance that a child will develop type I (juvenile) diabetes, which is a lifelong and irreversible condition that often is first diagnosed in adolescence. 

While the classic vitamin D deficiency disease is rickets (soft bones) in children, or osteomalacia in adults, recent research points to a strong association between low D levels and many other diseases.  At least 17 types of cancer may be related to D deficiency, including breast, colon and prostate cancer.  Osteoporosis and osteopenia, as well as incidence of fractures and incidence of falls in the elderly, are strongly associated with low D levels. There is evidence that lower D levels are associated with significantly higher rates of cardiovascular disease, including heart attacks and stroke, and with at least some autoimmune diseases, including multiple sclerosis and rheumatoid arthritis.  And vitamin D deficiency could play a role in higher levels of Type 2 (adult-onset) diabetes.  Low D levels apparently compromise immune function, and some researchers believe that the increased incidence of colds and flu in winter is related to lower D levels when sun exposure is reduced.  And low vitamin D levels are likely related to higher incidences of neck and lower back pain, fibromyalgia, psoriasis, fatigue, and cognitive impairment in the elderly.   

Vitamin D deficiency can be easily and precisely evaluated by getting a 25D blood test.  A healthy blood level is generally considered to be 40 to 70 ng/ml, with recent research indicating that levels near 60 or higher may be optimum.  Below 30 indicates significant deficiency.  Although supplement dosage varies depending on age, weight, skin coloring, and amount of sun exposure, recommended corrective doses of vitamin D may be about 10,000 IU/day if testing under 30ng/ml and 5,000/day if testing under 40, followed by a maintenance dose of at least 2,000 IU/day and, for some, as much as 5,000 or more.  Vitamin D experts recommend that children over the age of 1 without significant sun exposure take 1,000 IU/day, increasing to 2,000/day in their teens.  400 IU/day of drops in water or juice is indicated for newborns and infants unless their mother has high vitamin D levels.