Posted on May 13 2018
In Dr. Michael Greger’s book, How Not To Die, he routinely cites studies showing that vitamins and nutrition from whole foods is preferable to isolated vitamins in the form of a pill. But three new studies have thrown additional light on what taking mega doses of Vitamin D pills can (and can’t) do for you.
The recommended dietary allowance (RDA) for Vitamin D is 600 international units (IU) per day up to age 70, then 800 IU over age 70. These studies increased the dosage of Vitamin D to substantially more than these recommended levels to test the effect of mega doses on various bodily attributes.
- Insulin sensitivity. Researchers randomly assigned 18 people with obesity to a low-calorie diet with either a placebo or a dose of Vitamin D equal to 3,570 IU per day. Most had low blood Vitamin D levels to start with. After three months, insulin sensitivity improved only in the Vitamin D takers.
- Artery stiffness. Researchers randomly assigned 70 overweight or obese African-Americans aged 13 to 45 with low Vitamin D levels to take either a placebo or doses of Vitamin D at three different levels: 600 IU, 2000 IU, and 4000 IU. After four months, artery stiffness decreased in the groups that got 2000 IU or 4000 IU, but not in the other groups.
- Diabetes control. Researchers randomly assigned 127 people aged 25 to 75 (average age was 60) with stable type 2 diabetes to take 4000 IU of Vitamin D or a placebo. Only 26% of the participants had low blood Vitamin D levels to begin with. After 11 months, insulin secretion, insulin sensitivity and hemoglobin A1C (a long-term measure of blood sugar) did not improve more in the Vitamin D takers.
So, from these three studies it appears that mega doses of Vitamin D can improve your insulin sensitivity (study #1) but not necessarily (study #3). It may depend on your beginning level of blood Vitamin D, helping those with low levels more than those with higher levels. However, mega doses of Vitamin D do appear to help make arteries less stiff, which is good because stiff arteries can increase your blood pressure.
If your Vitamin D blood level is low (under 20 ng/mL) you may want to consider taking a mega dose of the vitamin. But be cautious, because some studies have shown a higher risk of falls at 2000 IU or more a day. If your Vitamin D blood level is not low, then you may want to consider taking a multivitamin or supplement (like Juice Plus capsules) with the RDA of Vitamin D because it is hard to get enough from food or the sun.
And, stay tuned. A much larger study looking at Vitamin D and more than a dozen conditions, called VITAL, is in progress. We will know more when the results of that study are published.