Recently the Institute of Medicine (IOM) came out with long awaited updated recommendations concerning the amount of Vitamin D supplements that Americans should be taking. Their recommendations surprised me somewhat (I thought they might be higher)-but first a little background information on Vitamin D.
While Vitamin D is traditionally referred to as a vitamin, it is physiologically a hormone which has significant effects on practically every organ in the human body due to the presence of Vitamin D receptors in many different types of tissue. Some researchers believe that low levels of Vitamin D can lead to heart disease, breast cancer, prostate cancer, colon cancer, diabetes, depression, and an overactive immune system, to name just a few diseases.
Some doctors have begun testing their patients’ Vitamin D levels as they hope that by correcting a low level they can help their patients to live longer lives and avoid common chronic medical conditions.
Vitamin D and Diabetes
Some research has also shown that a low Vitamin D level is associated with a risk for Type 2 diabetes. A few very small randomized controlled trials, lasting a year or less, have looked at the use of Vitamin D for the prevention or treatment of Type 2 diabetes by using very large doses of Vitamin D and they have reported variable results. These studies were so small that no conclusions have been drawn from them, and the role of Vitamin D supplements in the prevention or treatment of diabetes remains unknown.
Interestingly, a study completed at John Hopkins University discovered that 90% of their Type 2
diabetes patients had Vitamin D deficiency, or Vitamin D insufficiency. Meaning that doctors caring for Type 2 diabetes may decide to start screening their patients Vitamin D level.
Like many other medical conditions linked to Vitamin D deficiency, the role of Vitamin D remains controversial. It is possible that people who have diabetes, for example, have lower levels of Vitamin D as a result of their disease, and not as a precipitating cause. In this case correcting their Vitamin D level would not necessarily improve, or prevent, Type 2 diabetes.
Vitamin D and Cancer
Based upon research suggesting higher cancer rates with low Vitamin D levels, the Canadian Cancer Society recommends that adults take 1,000 IU of Vitamin D daily during the winter to decrease the risk of a number of different types of cancer, (and 1,000 IU year round for non-white residents). Perhaps most convincingly, an association between low Vitamin D levels and colon cancer was found in a group of patients who were followed over time with a blood test for their Vitamin D level.
Vitamin D and Heart Disease
The available evidence on Vitamin D levels and heart disease can sometimes appear to be contradictory. Nonetheless, some recent studies have demonstrated that increases in Vitamin D levels may reduce the risk of heart disease, and some cardiologists have begun testing patient’s Vitamin D level even though there is not yet evidence that Vitamin D supplementation decreases the risk of heart disease.
How Much is Too Little Vitamin D?
The IOM set the cut-off for Vitamin D deficiency at 20 ng/mL, stating that a Vitamin D level above this level is sufficient for good bone health and that most Americans achieve this benchmark. However, many researchers feel that a grey zone of between 21-30 ng/mL to be indicative of insufficiency and that levels above 30 ng/mL are desirable. Hence, many doctors are using 30 ng/mL as a cut-off, which the IOM believes is artificially increasing the percentage of Americans with Vitamin D deficiency.
The IOMs recommendations for the daily intake of Vitamin D have increased, from previously recommending that 200 IU (International Units) of Vitamin D for children and most adults, to 600 IU for most children and adults, and as much as 800 IU for the elderly (those over 70 years of age). The panel continues to endorse their recommendation that breastfed infants get 400 IU of Vitamin D a day as human breast milk does not contain Vitamin D.
This is a pretty big increase-by about three-fold-yet it is not going far enough for some doctors who themselves are taking 2,000 to 3,000 IU of Vitamin D a day and are recommending similar amounts of the sunshine Vitamin to their patients. How much is too much? The IOM has raised the maximum safe dosage of Vitamin D for adults to 4,000 IU a day from 2,000 IU a day.
Why didn’t the IOM go further?
Part of the reason for the IOM’s relatively conservative increase is due to the Vitamin E fad which excited the medical establishment years ago, I remember in 1997 being told by an internist that “We should all be on IV Vitamin E.” Things didn’t exactly turn out that way, and some studies have found that taking Vitamin E supplements is more dangerous than not taking them. So while the IOM agreed that more research needs to be done on Vitamin D-meaning that one day it may be concluded that everybody needs to have their Vitamin D level checked by the doctor-they concluded that there isn’t enough evidence yet to say that Vitamin D does anything other than prevent bone loss. This recommendation was made by the review of over 1,000 Vitamin D research articles, in addition to discussion with experts on the issue.
Also, while the recommended daily intake of Vitamin D has increased, the IOM has concluded that most people get enough Vitamin D in their diet (about 200 to 300 IU) and the rest via Vitamin D supplements and sunlight, and they don’t recommend that people get more sun (which can increase Vitamin D levels) due to the risk of skin cancer.
However, some people are predisposed to Vitamin D deficiency, such as those who live at higher latitudes, minorities with darker skin, the elderly, and people who live in urban environments as Vitamin D deficiency in these populations appears more frequently. Even being obese may predispose a person to Vitamin D deficiency as fat soluble Vitamin D may be locked up in the excess fat tissue.
As a medical student I saw two young African American children in Brooklyn who had rickets, possibly due in part to a combination severe lack of sunshine, Vitamin D in their food, and calcium. The lack of race specific guidelines offered by the IOM, in my mind, is worrisome.
While the IOM may assume that most Americans are getting enough Vitamin D, there could still be millions who are not. It seems to me that the IOM overall recommendations are in a way self-contradictory-if adults should get 600 IU a day, and if just 200 to 300 IU of that is coming from diet and the rest is coming from exposure to sunshine and the use of supplements, then shouldn’t we all be taking at least 300 to 400 IU of Vitamin D a day just to meet these guidelines in winter?
While just 10 minutes outside in summer during the midday sun (if you are fair skinned) will get you a lot of Vitamin D-about 10,000 IU-during winter due to the low sun and lack of penetration of UV B rays, going outside may not produce very much Vitamin D in the skin. Meaning that in the winter you may be relying on Vitamin D stores you have built up. And given that going outside during noon for ten minutes each day during summer will increase your sun cancer risk, why not just take a modest amount of Vitamin D each day?
Personally, I take about 1,200 IU of Vitamin D once a day year round. Ongoing clinical trials will likely shed more light on the ultimate actual benefit of taking Vitamin D supplements.
Robin L. Koffarnus, Pharm.D.
PGY-2 Ambulatory Care Resident
Blackstock Family Health Center
University of Texas at Austin College of Pharmacy
October 15, 2010