As most people know, adequate calcium intake is critical for maintaining bone health and preventing osteoporosis. Most people also know that adequate amounts of vitamin D is also critical for assuring the calcium will be absorbed. But what is enough vitamin D? The research coming out the last few years is finally answering that question.

The issue of how much vitamin D to take is only an issue because we don’t live the way we evolved. Remember, unlike all other vitamins, vitamin D can be created in our own bodies. It is created in our skin from a cholesterol precursor by contact with ultraviolet radiation (UVB) from good old sunlight. Our human ancestors, if we go back many many years, spent most of their lives outside in the sun and mainly in low latitudes such as the tropics. Without clothing to get in the way this kind of sun exposure created plenty of vitamin D, far more than the average American gets. Now we spend most of our time indoors, when in the sun our skin is protected by clothing or sunscreen, and many of us live above the 35-degree latitude where the angle of the sun limits the exposure of ultraviolet light.

There are several factors that influence calcium absorption but the first step is to ingest enough. The current recommendation for osteoporosis prevention is that a woman over 50 should get 1200 mg of calcium per day from food and supplements (1000 mg for women 50 and under and the same for men). However, calcium alone does not maximize the potential for maintaining bone health. Other factors include magnesium, manganese, zinc, copper, boron, strontium, silicon, vitamin K, folic acid, vitamin B12, vitamin C and, of course, vitamin D.

People absorb in the range of 15 to 45% of the calcium ingested. Recent research shows that low amounts of vitamin D means that your absorption is going to be around the 15% range and adequate amounts of vitamin D will put your absorption around the 45% range. That is three-fold difference in the amount of calcium your body absorbs from the ingested calcium in the food and supplements. That is likely to be the difference between getting osteoporosis and not.

So what is enough vitamin D? The historical recommendation of 200 I.U.s of vitamin D per day (400 for women 50 and older) came from clinical experience that this amount was enough to prevent rickets. Until fairly recently there was no way of directly measuring the level of vitamin D in the body. Consequently, there was no way to thoroughly study what intake levels were adequate to prevent disease. Now that blood (serum) levels can actually be measured we have seen an explosion of published research in the last few years.

Previous “normal” ranges of serum 25-hydroxycholecalciferol (commonly called 25(HO)D – the measure of vitamin D in the serum) of less than 20 ng/mL were considered to be a deficiency. However, the latest research shows that a minimum of 32 ng/mL is necessary for adequate calcium absorption. That is quite a difference.

By the end of the summer outdoor workers in temperate latitudes like ours have serum levels of 60 ng/mL. People who live in the topics and spend a lot of time outdoors have levels higher than this all year-round. Clearly the old standard for “normal” levels of serum vitamin D are too low!

Vitamin D lasts about 60 days in the body so even people who have gotten plenty of sun in the summer will start becoming deficient by late fall in latitudes above 35 degrees, such as the Midwest. We could all move to the topics but supplementation is probably more practical.

Vitamin D is an oil soluble vitamin so too much can be toxic. The Institute of Medicine says that 2000 I.U.s of vitamin D per day is the upper limit of safety. However, this is another one of those old numbers that is no longer consistent with the research. Research shows that during the winter months it takes 5000 I.D.s per day from food or supplementation to get to the 60 ng/mL that is normally found in the serum of those outdoor summer workers. Another study found that it took 40,000 I.U.s per day to get up to serum levels associated with toxicity. 

It is clear to me, and many other people, that the maximum safe dosage of vitamin D is much much higher than 2000 I.U.s per day currently recommended by the Institute of Medicine. Even some dietitians who work in calcium research are now saying that 3500 to 5500 I.U.s a day from all sources is required to maintain adequate serum levels of vitamin D. However, it is important to note that you can take too much vitamin D. The main clinical sign I have seen that someone is taking too much is calcium blood level abnormalities. I recommend that anyone routinely taking over 4000 I.U.s a day should periodically get both their vitamin D and calcium blood levels checked.

What about getting your vitamin D from sun exposure? It is often recommended that if you get direct sun exposure throughout the year you can maintain adequate levels of vitamin D. The recommendation varies depending on the source – I’ve seen recommendations vary from 20 minutes of exposure to face and arms twice a week to10 to 15 minutes daily to 40% of your skin surface. Non-sunburning sun exposure is clearly a good idea – it is the natural way to get your vitamin D. However, this will probably be inadequate to maintain vitamin D reserves unless you live in the tropics year-round. And it is simply impossible if you live in Nebraska or any other area that is above 35 degrees latitude (Omaha is 41 degrees north). In addition, dark-skinned people need even more sun exposure to get the same amount of vitamin D production. So if you live here, sun exposure alone isn’t going to do it.

Current research shows that during the autumn, winter and spring an intake of vitamin D in the standard recommended doses of 200 to 400 I.U.s per day will not produce the minimum level of serum 25(HO)D necessary for healthy bones. That means that almost no one in this region of the country (man, woman or child) has adequate serum levels of vitamin D. What a surprise that as so many women reach middle age they are being diagnosed with osteopenia and osteoporosis.

For osteopenia and osteoporosis patients I am now recommending 2000 to 4000 I.U.s per day of vitamin D when there is little summer sun exposure (along with calcium and the other healthy bone cofactors). If you don’t spend much time outdoors in the summer without sun protection, supplementation would need to be year-round. It is also advisable for these patients to get their serum 25(HO)D level check periodically to make sure it is staying above 32 ng/mL. For many reasons (see below) every adult, men and women alike, should be getting more vitamin D than is common today. Finally, supplementation must be with D3 (cholecalciferol – the natural human form) and not D2 (ergocalciferol – as found in “vitamin D” enriched milk).


The benefits of adequate amounts of vitamin have been all over the news. New studies are being published almost everyday. Here is a summary of some of it:
*  Overall reduction in mortality. One meta-analysis (a study of many studies) showed a 7% lower risk of death overall during the six-year period studied.
*  Improved immune function. One study showed a drop in colds and flu by 70% over three years with supplemental vitamin D. The natural loss of vitamin D reserves in the autumn corresponds directly to the onset of the cold and flu season. Is this the reason there are so many more infections in the fall and winter?
*  Reduction in heart disease.  Those who supplemented with vitamin D had a 31% lower risk of dying of heart disease in one study. Another found patients with chronic heart failure had lower levels of vitamin D than others. Vitamin D has also been associated with reducing blood pressure.
*  Less cancer risk. Both breast and colon cancer has been shown to be less likely with adequate amounts of vitamin D. A study on colon cancer showed that those with higher serum levels of vitamin D had a 72% less chance of dying from colorectal cancer than those people with the lowest levels.
*  Reduced diabetes and insulin resistance. Babies supplemented with vitamin D in Finland the first year of life had over 80% reduction in the risk of getting type I diabetes. Another study showed that adequate serum levels of vitamin D compared to those without showed 60% less insulin resistance, which leads to less metabolic syndrome and less type II diabetes. Plus normal insulin secretion is dependent on vitamin D.
*  Lower risk for MS. A study showed a 40% lower risk for MS in those who supplemented vitamin D. Another suggested that those who spend more time in the sun had lower risk than those that stayed out of it.
*  May help prevent inflammatory diseases like rheumatoid arthritis and inflammatory bowel disease (Crohn’s disease, ulcerative colitis, etc.).


*  No one living in the higher latitudes should supplement with less than 1000 I.U.s of vitamin D per day unless it is the summer and they are out in the sun without protection regularly. For many people, if not most, it should be higher amounts. Researchers are currently calling for changing the recommended doses to a range of 1000 to 2000 I.U.s per day (to be adjusted for summer sun exposure).
*  Women (or men) with osteopenia and osteoporosis should be taking at least 2000 to 4000 I.U.s of vitamin D per day (along with calcium and the other healthy bone cofactors).
*  When possible get your serum 25(HO)D level checked periodically to make sure it is staying above 32 ng/mL.
*  Only supplement with D3 (cholecalciferol); never D2 (ergocalciferol).

We offer nutritional consultations for people who would like an individualized supplement regimen, or to have their nutritional supplements reviewed for their appropriateness, potential conflicts with any pharmaceutical medications needed, and their cost-effectiveness. If interested contact the office.