We all know that Vitamin D is important for bone health. Lately a lot of attention has also been focused on Vitamin D’s effect on numerous major diseases, namely cardiovascular disease, diabetes, cancer, immune disorders, as well as muscle strength, weight and even long term mental acuity.
Vitamin D level is measured in our blood as a 25-hydroxyvitamin D. This represents the conversion of provitamin D to previtamin D in the skin during exposure to sunlight emitting ultraviolet radiation. Previtamin D is then converted in the liver to 25-hydroxyvitamin D. About 40 to 50 % of circulating 25-hydroxyvitamin D is derived from skin conversion. We also can get some vitamin D from food sources. (Usual amounts are between 100 and 200 IU’s or international units a day.) I know this all sounds a bit confusing, but in a nutshell (and nuts don’t have a lot of D, but if you are out there harvesting them in the sun, your D levels will benefit.) serum 25-hydroxyvitamin D is the best indicator of our overall Vitamin D status. It reflects the D from nutritional intake and sunlight exposure. The latter is of course dependent on latitude (less in northern latitudes), the season, clothing, sunscreen use and local weather conditions. Then there is the issue of pigment…the darker a person’s skin the less she or he will absorb the requisite UV rays. Levels of 25-hydroxyvitamin D are lower in blacks than whites who live in the same environment. Body mass also seems to matter; heavier individuals typically have lower levels than their svelter counterparts. Other conditions that can also result in low 25-hyroxyvitamin D levels include: poor dietary intake of Vitamin D together with negligible sun exposure (this probably represents many of us), malabsorption due to inflammatory bowel disease, gluten intolerance, gastric surgery, liver disease, intestinal overgrowth (of bacteria) use of anti-seizure medications and long-term use of steroids.
So what is a normal D level, and what should we do to ensure that it is high enough? Currently “frank” Vitamin D deficiency is considered to be less than 10 ng per milliliter; Vitamin D levels between 10 and 30 are “insufficient” and “normal” D is defined as blood levels between 30 to 79 ng per milliliter. Alas, when this range is used, the estimated prevalence of Vitamin D deficiency includes 50 to 80% of the general population!
A case vignette which highlights Vitamin D levels and need for supplementation appeared in the January 20, 2011 New England Medical Journal. In this article the author described a healthy 61 year old white woman whose level of 25-hydroxyvitamin D is 21 ng per milliliter; she is not overweight , has never had a fracture and her bone density at the hip is -1.5. What should she do (if anything)?
The first concern that the article dealt with was her current and future bone health. Most of the studies that the author cited suggest that calcium plus vitamin D (and not Vitamin D alone) is marginally effective in reducing the risk of fracture in older patients compared with no supplementation. But he didn’t feel she was old enough or at sufficient risk to require high doses of Vitamin D supplementation. (See the end of this report.)
He then addressed Vitamin D’s “other health effects”, and that “observational studies in large cohorts have shown significant associations between low levels of 25-hydroxyvitaminD (i.e. below 20 ng per milliliter) and an increased risk of metabolic, neoplastic (cancer), and immune disorders such as type1 diabetes mellitus and multiple sclerosis. …That two conditions often connected with low levels of vitamin D are atherosclerosis and diabetes mellitus.” But then the author goes on to state that “there are not enough data from large, randomized, controlled trials to assess whether Vitamin D supplementation reduces the risk of chronic diseases other than osteoporosis.” (Please don’t be turned off by this, nearly every study that is published, especially if it does not include the entire diverse population of the US followed for their lifetime’s ends with this statement.)
The article then deals with “areas of uncertainty”, which basically include all other medical disorders and diseases and the potential benefit of Vitamin D supplementation to prevent or diminish their occurrence. The author once more refrains from advocating Vitamin D to ward off disease, writing “data are lacking from large randomized, controlled trials designed to determine whether Vitamin D supplementation reduces the risk of other major diseases, such as colon cancer.” (For which there are observational data suggesting a reduction in risk with supplementation).
We will get future information with an ongoing study called the Vitamin D and Omega-3 Trial (yes it has an acronym…VITAL) which is a 5 year, randomized, placebo-controlled study involving 20,000 US men and women . The goal is to see whether Vitamin D supplements (2000 IU per day) with or without supplements of n-3 fatty acids helps prevent cancer and cardiovascular disease.
So should we wait until this and other studies have been completed….and will they be enough for “orthodox”, peer reviewed and New England Medical Journal published recommendations? The answer may not give us an A on any medical exam but then neither do we want a grade lower than that D when it comes to our future health…
To continue this Vitamin D review: There are 2 kinds of oral D supplementation. The usual over-the-counter D comes in the form of D3 and generally is available in doses of 400, 1000 and even 2000 units. A second type of D, called D2 is available by prescription. D2 has 1/3 the “power” of D3. Toxicity from overdoses of D3 is rare and generally will not occur with doses less than 10,000 IU a day. The Institute of Medicine (IOM) has recently set the tolerable upper level of daily Vitamin D (3) at 4000 IU. One reason for their concern is that there have been recent observational studies that suggest that blood levels of 25-hydroxyvitamin D over 60 ng per milliliter may increase risk for pancreatic cancer, vascular calcification and death from any cause. Too much of a good supplement (or its associated blood level) may not be a good thing.
To complicate the issue … an international workshop on Vitamin D in 2007 agreed that most of the world’s population is not getting enough Vitamin D to maintain healthy bone and minimize fracture risk. In 2010 the International Osteoporosis Foundation recommended a target blood level of 25-hydroxyvitamin D of 30 in all elderly persons, stating that vitamin D intakes as high as 2000 IU per day may be necessary to attain this recommended level. But to make this more confusing to “D attentive” physicians and patients, the IOM has recently stated that, based on observational studies and recent randomized trials, a serum level of 20 ng per milliliter of 25-hydroxyvitamin D would protect 97.5% of the population against adverse bone outcomes such as fractures and falls.
After considering these conflicting studies, the author of the NEJM recommends that the woman in the vignette maintain an exercise program, make sure to have a total calcium intake of 1200 mg a day (though food and supplements) and since she is not at high risk for a fall, take just 600 IU of Vitamin D a day.
Having looked at this article (and many other studies that I will not burden you with…) I suggest that my patients take 1,000 IU to 2,000 IU of D3 a day and would suggest that the woman in the vignette do the same. My preference is that we all reach a blood 25-hydroxyvitamin D level of at least 30 ng per milliliter. But of course neither I, nor any physician can promise good bones or disease-free health through Vitamin D supplements.