The studies keep pouring in about the benefits of vitamin D. We now know it’s essential for the heart, bones, and nearly everything in between, and it also protects against diseases such as cancer and diabetes. Here are just two of the many studies that show why you need to boost your intake.
- Researchers collected information on the serum vitamin D levels of 1,000 Italians over age 65 and then followed their health outcomes for an average of 6.5 years. The results: Those with lowest levels of vitamin D (less than 10.5 ng/mL) were at increased risk of dying from cardiovascular disease or other illness.
- British researchers performed the first ever meta-analysis of studies looking at serum vitamin D and the presence or absence of “cardio-metabolic diseases” (metabolic syndrome, diabetes, and cardiovascular disease). Twenty-eight studies were reviewed, involving 100,000 men and women. The results: Individuals with the highest levels of vitamin D (more than 26.5 ng/mL) were 33 percent less likely to have heart disease, 55 percent less likely to have diabetes, and 51 percent less likely to develop metabolic syndrome.
Vitamin D3 Testing
Vitamin D3 has a pretty crowded bandwagon these days, and that's a good thing. More and more doctors are recommending that their patients take a vitamin D supplement, and are ordering tests for vitamin D. Unfortunately, too many doctors are ordering the wrong test. (Sorry, I have to get a little technical here for the next section. There's no way around it.)
- 1,25-dihydroxyvitamin D3 is the only known active metabolite.
- Tests for 25-hydroxy lump together measurements for the D2 and D3 forms. And, of course, only the D3 form is beneficial.
- The conversion from 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D occurs in the kidneys. Even if the other problems with the 25-hydroxyvitamin D test didn't exist, the test would still miss any difficulties with conversion. (And given the high prevalence of kidney disease in our society, primarily from hypertension or from diabetes, I wouldn't want to rely on a measurement of pre-kidney levels.)
- Serum levels of all forms of 25-hydroxy are subject to greater fluctuation than are levels of post-conversion 1,25 dihydroxyvitamin D. Acute exposure to sunlight or consumption of a vitamin-D fortified food can create a spike in readings, which might be spot accurate but could give a misleading impression of overall vitamin D status.
The "normal range" is so broad that it's practically meaningless, though. For the 1,25 dihydroxyvitamin D test it's 42 to 165 picomoles per liter (pmol/L). You can assume that, unless you spend a significant amount of time in the sun most days, then you are vitamin D deficient.
Vitamin D3 Intake
The current dietary guidelines still recommend 400 IU of vitamin D, but the research now available clearly shows that number is way too low. The minimum recommended daily intake should be:
- 1,000-3,000 IU if you are healthy,
- 5,000-10,000 IU taken for three months if you have low levels of vitamin D, then recheck your levels.
In general, the only people who need to check with their doctors and possibly limit their intake of vitamin D are those with adenoma of the parathyroid gland, granulomatous diseases, lymphoma, sarcoidosis, and tuberculosis. These conditions may cause the body to produce too much vitamin D, putting you at risk of developing an elevated calcium level. But the rest of us can’t get enough vitamin D. Intake of up to 100,000 IU per day for months at a time has been shown to be safe for most people—though I don't recommend that much--so you don't need to worry about accidentally overdoing it.