Debunking the latest “fake news” about vitamin D

Plus, why September is the perfect month to get your D levels tested

As the summer comes to an end, it’s more important than ever to keep your vitamin D levels elevated.

From October to March, the sun will no longer get high enough in the sky to activate your skin’s natural synthesis of vitamin D. So it’s critical for your health to supplement with this essential vitamin—despite what you may have heard.

In recent months, vitamin D supplements have been gaining the wrong kind of attention. Maybe you’ve seen headlines about how “too much vitamin D can be a bad thing,” or articles citing highly questionable studies on D’s supposedly deleterious effect on the body or brain.

But today, I’d like to set the record straight. Here’s what you really need to know about the recent “controversial” studies on the sunshine vitamin.

How much D do you need?

The first study purportedly analyzed how three different doses of vitamin D affected cognitive outcomes in postmenopausal, overweight women.1

All study participants were randomly assigned to take three different doses of D: 600 IU, 2,000 IU, or 4,000 IU daily, for one year. (Note that these dosages are much less than the 10,000 IU other studies have found to be optimal for reducing the risk of many chronic diseases.)

At the beginning and end of the study, researchers measured each woman’s levels of vitamin D, hormones, and amyloid beta (a factor that some scientists think is significant in Alzheimer’s disease).

But the researchers only tested the women’s mental function at the end of the study. Meaning any cognitive effects of D can’t be compared on a normal before-and-after basis—which is the whole reason for doing a clinical trial in the first place!

The women had average starting D levels of 27 nanograms per milliliter (ng/mL). Over one year, their D levels increased to:

  • 30 ng/mL in the 600 IU group
  • 36 ng/mL in the 2,000 IU group
  • 41 ng/mL in the 4,000 IU group

But none of the women were able to achieve the optimal 50 to 60 ng/mL levels— illustrating that even 4,000 IU of D a day is much too low for good health.

In addition,  the participants who took 2,000 IU of D daily performed significantly better on learning and memory tests compared to the 600 IU group.  However, researchers reported that the 4,000 IU group had a “slower reaction time” than the 600 IU group.

But in my view, because the researchers didn’t do before-and-after cognitive tests on the study participants, it sounds like they led a “dose-finding” study to see how different D doses influenced overall D levels.  And then they tacked on the cognitive measurements after the study was completed.

What really causes bone breaks

As a result, the only clear and sensible finding in this limited study was that higher doses of D resulted in better learning and memory test performance—even when the doses were well below optimum.

But some articles about this study only highlighted the slower reaction times associated with the 4,000 IU dose—concluding that “too much” vitamin D may be linked to an increased risk of falls or injuries.

This is a completely ignorant, irresponsible take on this otherwise unremarkable study. In fact, plenty of research shows that bones are more likely to break when women (and men) have suboptimal, lower levels of vitamin D—not “too much.”

Also, ironically, in older women, it’s not that they fall and then break a bone. It’s that a weakened bone simply breaks, and so they fall.

Therefore, the real finding is this: Higher, optimal D levels prevent bone breaks and falls.

Is vitamin D bad for your kidneys?

It’s not often that medical literature reports on a single case of anything. Usually, scientific journals demand so-called “gold-standard,” evidence-based studies on multiple people. But that rule seems to be readily suspended when it comes to attempts to discredit vitamin D.

One Canadian study reported on how a 54-year-old man went to the doctor with signs of kidney damage.  He had just returned to Canada from a trip to Southeast Asia, where he had suddenly gone from getting very little D in the great white north, to sunbathing six to eight hours per day for two weeks in the tropical sun.

The man was already being treated with drugs for cholesterol, high blood pressure, and gout. He also had a strong family history of kidney disease.

His physician wisely discontinued the blood pressure drugs and diuretics, which can be damaging to the kidneys—especially with the probable heat exposure and dehydration the man experienced in Southeast Asia.

But the patient continued to show signs of kidney toxicity. Doctors then discovered he had been taking 8,000 to 12,000 IU of vitamin D for two and a half years. They also found that his blood levels of D were unusually high.

The conclusion was that these supposedly “high” doses of D led to kidney disease—despite all the man’s long-term risk factors mentioned above.

Not to mention his short-term risk factors… After all, the man had just gone from subarctic Canada to tropical Southeast Asia, ramping up his vitamin D production to higher than any dietary supplement could deliver.

The real lesson from this study is to avoid cholesterol drugs, which damage the kidneys and other organs. Instead, practice non-drug methods for controlling blood pressure, like following the Mediterranean diet.

This diet consists of plenty of fresh fish, free-range meat, nuts, seeds, legumes, fruits, vegetables, and full-fat dairy (such as butter, cheeses, and yogurt). (I’ll tell you more about reducing your blood pressure and risk of heart disease, without drugs, in October’s newsletter.) And, of course, if you have a family history of kidney disease, you and your doctor should be extra careful.

So putting aside this highly unusual case, there’s no real reason to go against all of the other research showing that 10,000 IU of vitamin D a day is best (and safe) for optimal health.

Believe it in your heart: You need D

Last but not least, let’s look at yet another study that was blown out of proportion by the mainstream. When in reality, all it really showed was that miniscule doses of vitamin D are useless in protecting against heart disease. Gee, what a surprise!

As you know, studies consistently show that vitamin D decreases your risk of cardiovascular diseases by directly influencing heart calcium, muscle relaxation, and heart function—and reducing the risk of blood clots.

But a young doctor decided to set the world straight and get his name in the headlines by claiming that vitamin D has “no effect” on heart disease.

The doctor, who was only a hospital resident when he conducted his analysis, purportedly reviewed a staggering 7,816 studies. But, he cherry-picked just 21 studies for his final analysis.

The vast majority of the studies he chose used pathetically low doses of vitamin D—100, 300, 400, or 800 IU daily. Four of the 21 studies used daily doses of 1,000 IU. Two used 2,000 IU, and one used 4,000 IU.

Furthermore, large numbers of participants in the studies were also prescribed calcium supplements—which, as I often report, increase your risk of heart disease.

Also, given the widespread D deficiency in the U.S., study participants likely didn’t have optimal D levels to start with—and certainly weren’t getting enough sun exposure, or supplementation, to correct it.

Get your blood tested this month

Despite all of these shortcomings, some of the studies did show benefits of vitamin D for heart and cardiovascular diseases—and a trend for reduced cardiovascular events in older people. But these were buried behind all the junk studies the young doctor included in his analysis.

Still, at the end of the day, the real lesson is nothing new: Don’t use doses of dietary supplements that are too low!

Instead, ask your doctor to measure your vitamin D levels this month, at the end of summer, and again at the end of winter. (Remember, you’ll want to achieve blood levels of 50 to 60 ng/mL.) And then, discuss supplement doses based on your blood levels, medical history, health conditions, and treatments.


1“Three Doses of Vitamin D and Cognitive Outcomes in Older Women: A Double-Blind Randomized Controlled Trial.” The Journals of Gerontology: Series A, glz041,

2“Use of vitamin D drops leading to kidney failure in a 54-year old man.” Canadian Medical Association Journal, 191(14): E391-394, April 8, 2019.

3“Vitamin D Supplementation and Cardiovascular Disease Risks in More Than 83 000 Individuals in 21 Randomized Clinical Trials: A Meta-analysis.” JAMA Cardiol. Published online June 19, 2019.