Recent research has led to the dramatic conclusion that a relative deficiency of vitamin D causes risk for many illnesses. Many of these diseases are increasing, and scientists have noted that they are much more frequent in people with lower Vitamin D levels, actually the pre-hormone 25-hydroxy-D.

Vitamin D is important in the absorption from food and retention of calcium in bones. However, many people are unfamiliar with other functions of this vitamin/hormone. It also is important in stimulating and calming certain immune cells, and fighting infection. In fact, immune cells use vitamin D activation to turn on production of infection-fighting natural antibiotic molecules. People who are vitamin D deficient are also susceptible to both common mild respiratory illness (cold, bronchitis), as well as severe infections such as tuberculosis, mononucleosis, and influenza. Vitamin D levels less than 30 are also strongly associated with osteoporosis (weak bones) and risk of fractures, especially in older people. Bone density (DEXA) tests are used to diagnose osteoporosis. A T-score of more than 1.5 is a significant risk of fracture. Smaller people, especially women, Caucasians, and those going through early menopause usually suffer from osteoporosis. This can lead to painful or disabling hip or back fractures. It seems to have been a dogma that you can get too much vitamin D, and this has always led to conservative recommendations. However, the concerns are now being overcome that the far greater problem is lack of adequate vitamin D. Exceedingly high doses of vitamin D, such as are used in rat poison, are far beyond those generally consumed by people.

Many people are aware of the need in children in order to prevent a deforming bone illness called rickets. Rickets was virtually eliminated in North America by adding small amounts of vitamin D to milk, and in Europe by laws requiring children to play outside in the summer without clothes (really!).

Vitamin D comes from two sources, sunshine and diet. People who live in the sun daily throughout the year do not need vitamin D supplementation. Since very few of us are lifeguards or work in fields year round, most of us need to take care to get enough of the “sunshine vitamin.” We were always told that we needed to drink milk to get vitamin D. Unfortunately, the amount required is much greater than we consume. To barely get enough vitamin D to live (800 U), one has to drink 8 glasses. Fish is an excellent source, and 3 oz of tuna has 200 U. However, it takes quite an effort to obtain enough vitamin D from diet.

Most vitamin D comes from exposure of our skin to the sun (the same ultraviolet irradiation which can cause sunburn and skin cancers). A 30 min full body exposure to noontime summer sun triggers the release of 20,000 units. Judicious use of sunshine with protecting the skin is an important way to assure enough vitamin D. However, most of us choose to stay indoors most of the year and protect our skin from the sun with clothing and sunscreen.

The exact benefits and needs for Vitamin D in people are still unclear. Vitamin D metabolism, genetics, and needs are an active area of research, and the following recommendations are based on expert opinion, and not as much on proof from research.

Vitamin D deficiency has also been implicated in susceptibility to cancer, influenza, fibromyalgia, multiple sclerosis, systemic lupus, and rheumatoid arthritis. Dr. Edward Giovanucci of Harvard School of public health fells that certain cancers and immune dysfunction are strongly associated with vitamin D deficiency. He found prostate cancer and low blood levels of vitamin D (specifically, of proteins produced as vitamin D is metabolized). The more unlucky men had variations in genes involved in vitamin D processing and were more than twice as likely to develop aggressive, deadly prostate cancers. Moreover, more than two-thirds of the nearly 15,000 men in his study were deficient in the vitamin. Populations with adequate vitamin D levels have about half the risk of colon cancer as people who don’t get enough. Other cancers have been linked to lower vitamin D levels, too, particularly those of the digestive tract. People who live in the North (or the South in the Southern Hemisphere), are more susceptible to these cancers. Dark skinned people are likewise at greater risk, as a given amount of sun produces only half as much vitamin D in dark-skinned people.

Traditionally, 800 units per day from the diet were recommended, but we now know that 5000 U are required by adults (1,000 U/day for every 25 pounds weight in children). Many doctors recommend 2000 units a day, or more. However, recent evidence that even these supplements are inadequate for most of the year for nearly half of people. Doses of 10,000 units a day have been proven safe. Why? Because the “vitamin” is not the active hormone form of vitamin D. We use up the vitamin in our body by 50% every two weeks when we stop getting it from sun. It undergoes two stages of activation to do its job in the body, and this is closely regulated. The widely used calcium and vitamin D supplements are helpful, but likely not adequate to meet the new recommendations. Vitamin D supplements of high potency (1000-5000 units per capsule) are recommended to meet these new recommendations. If vitamin D (usually sold as D3) is taken in larger doses without calcium, it can be taken in any reasonable fashion, daily or weekly. Currently, capsules with 5,000 IU are widely available. One must check carefully the bottle when purchasing vitamin D, as it comes in sizes from 400 to 5,000 units per capsule.

A research trial published in 2010 showed children taking 1,200 U D3 daily in winter were 42% less likely to get infected with seasonal flu.

Judicious sunshine exposure, year round if possible, is recommended, for a total of 40 minutes within one week of full body (as practical) sunshine exposure. It is not necessary to tan, get hot, or burn, and the sun is effective even during early or late parts of the day, and even on overcast days. It is important to expose as much skin as possible and not to burn. Tanning beds do not have the right type of UV light, but still damage the skin.

 As a neurologist, this has greatly affected how I practice, as it has been seen that multiple sclerosis, a fairly common and serious disabling illness is strongly associated with low vitamin D levels. Not each person has low levels, and those with higher levels are usually less severely affected. People affected with MS have lowered vitamin D levels (as measured by 25-HO-vitamin D), than others in the population, and people with very high vitamin D levels seem to almost never get multiple sclerosis. A genetic cause of this vitamin D deficiency is likely, and people with MS may “waste” vitamin D. Most people which we see with MS are vitamin D deficient when we test them. Similar findings are present for rheumatoid arthritis and Crohn’s disease, other immune diseases which share the same risks.

The target level of 25-hydroxy-vitamin D in the blood is more than 60 ng/dl. This is twice the currently recommended level for bone health. It is possible but difficult to take too much vitamin D. A toxic level of vitamin D is usually 200 or over (150 is the upper limit to avoid toxicity). Excess vitamin D results in too much calcium in the blood with tiredness and fatigue, and can predispose to kidney stones. We recommend vitamin D levels be checked in the late winter/early spring (March) as they are lowest at this time. The level should be checked any time there is a suspicion of too much vitamin D.

The message is to strongly consider supplementation with vitamin D3 5,000 U a day in adults, and as above for children, to assure any ill effects of a deficiency are avoided as much as possible. Great care should be used in obtaining sufficient sun exposure so as to avoid sunburn, which predisposes to skin cancer. Attention to children obtaining sufficient vitamin D may lead to preventing many serious infections and immune illness, as well as assuring strong bones and less fractures later in life.

Dr. Samuel F. Hunter, M.D., Ph.D. practices at Brain and Nerve Neurology in Franklin, Tennessee, and directs the advanced Neurosciences Institute (http://neurosci.us) and the NeuroNexus Neurology Education and Research Center (http://neuronexus.org). Follow him on twitter at NeuroNexus1.