The People's Perspective on Medicine

Why Don’t Vitamin D Supplements Work as Expected?

Vitamin D supplements are extremely popular. Millions swallow little golden pills daily. But why are clinical trials producing such disappointing results?

If you are taking big doses of vitamin D in the hopes of staving off all sorts of health problems, you may be disappointed. Most research has not demonstrated that taking high doses of vitamin D supplements will improve health. Why Not?

The Fascinating Vitamin D story:

Vitamin D leads a double life. In addition to being a crucial vitamin, it is also a hormone that affects every cell in the body.

For years, health professionals thought that this nutrient was responsible primarily for building strong bones. When there was a deficiency in vitamin D, children developed rickets. In this condition, bones are fragile and can become deformed, resulting in bowed legs and thickened wrists.

Over the last several decades, scientists have discovered that there are vitamin D receptors throughout the body. People who are deficient in vitamin D are more susceptible to a wide range of disorders, from arthritis and heart disease to diabetes and cancer. Researchers report that when circulating levels of vitamin D are low, people are more susceptible to respiratory infections and more likely to die prematurely (Circulation Journal, April 20, 2017).

Health Problems Linked to Low Vitamin D Levels:

  • Asthma in children
  • Autoimmune disorders such as multiple sclerosis
  • Cancer
  • Cardiovascular disease (heart attacks, etc)
  • Cognitive impairment (Alzheimer’s disease, dementia)
  • Diabetes
  • Erectile dysfunction
  • Fractures, osteopenia, osteoporosis
  • High blood pressure
  • Infections (pneumonia, colds, etc)
  • Mental illness (depression, schizophrenia)
  • Psoriatic arthritis

Vitamin D Supplements: A Puzzling Paradox

What has scientists confused is why vitamin D supplements haven’t prevented some, or all, of these serious health conditions. Why aren’t vitamin D supplements working as expected?


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Vitamin D and the Sun:

For thousands of years, humans have gotten their vitamin D through sun exposure. When ultraviolet rays hit the skin a precursor of the hormone (cholecalciferol) is formed and absorbed. The kidney converts it into the active form of vitamin D.

There is tremendous variability in the amount of vitamin D the skin will make. It depends in part on the intensity of the sun, the time of day and skin type. Your body can make between 10,000 and 25,000 international units of vitamin D in less time than it takes to develop a sunburn. Sunscreen blocks the natural formation of vitamin D from the sun.

The body carefully regulates its production of vitamin D. You can’t overdose on vitamin D through sun exposure (Institute of Medicine, 2011).

Researchers have noticed the problems associated with low levels of vitamin D. They have conducted many experiments to see how well supplements of vitamin D can treat the disorders connected to vitamin D deficiency.

Vitamin D Supplements and Disappointing Results:

A study in the European Heart Journal, May 12, 2017 reported that vitamin D supplements “did not reduce mortality in patients with advanced HF [heart failure].”

Research published in BMJ Open (online, Oct. 23, 2013) found that vitamin D supplements did not help patients with a severe autoimmune condition called sarcoidosis.

High use of vitamin D supplements did not lower the risk of early menopause Nurses’ Health Study II). This was published in the American Journal of Clinical Nutrition (May 10, 2017). When these women got their vitamin D from food, however, there was a modest reduction in early symptoms of menopause.

High-dose vitamin D supplements were not beneficial for overweight, vitamin D deficient patients who were diagnosed with type 2 diabetes (American Journal of Clinical Nutrition, May 10, 2017). The authors concluded that it would be unlikely that vitamin D supplements

“would be an effective strategy for reducing diabetes risk even in vitamin D-deficient populations.”

Other studies have also yielded disappointing results. A recent example is a study published in The Lancet Diabetes & Endocrinology (April 28, 2017).

The investigators recruited more than 5,000 volunteers in Auckland, New Zealand, for a placebo-controlled trial. Half of them were given cholecalciferol (vitamin D3) at a dose of 100,000 IU once a month. The other half got a placebo once a month. All of the participants kept track of any falls or fractures they experienced during the three-plus years the study continued.

The investigators didn’t find any differences between the two groups, whether in falls, fractures or death. They concluded that this form of supplementation was ineffective. To give them credit, however, they noted: “Further research is needed to ascertain the effects of daily vitamin D dosing, with or without calcium.”

Daily Dosing: How Important?

We too would like to see more studies with daily vitamin D dosing. We suspect that one reason so many studies that use enormous doses once a month or even once every few months haven’t shown benefit is that the scientists are taking the wrong view of this vitamin.

They are treating it as if it were a drug. But a hormone that is intimately involved in so many processes in the body might not behave like a drug at all. The body may not respond normally to such a high dose. In nature, the body gets a smaller amount every day. And the body regulates that natural vitamin D quite effectively. It may also be that the vitamin D (and its derivatives) made by the body from sun exposure work differently in the body than the oral vitamin D supplements so many people take.

To learn more about this crucial hormone, you may wish to read our Guide to Vitamin D Deficiency. It can be downloaded from our website.

Anyone who would like a printed copy, please send $3 in check or money order with a long (no. 10) stamped (70 cents), self-addressed envelope to:

  • Graedons’ People’s Pharmacy, No. D-23
  • P. O. Box 52027
  • Durham, NC 27717-2027.

Share your own experience with vitamin D supplements in the comment section below. If you found this information of interest, please vote at the top of the article.

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About the Author
Joe Graedon is a pharmacologist who has dedicated his career to making drug information understandable to consumers. His best-selling book, The People’s Pharmacy, was published in 1976 and led to a syndicated newspaper column, syndicated public radio show and web site. In 2006, Long Island University awarded him an honorary doctorate as “one of the country's leading drug experts for the consumer.” .
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I’ve taken 10,000 IU of vitamin D for close to 4 weeks now and began experiencing dizziness and heart palpitations. While it has improved since stopping the supplements, it still persists. I can’t figure out how to get my body back on track! All of this is the result of the misinformation from a naturopath.

Part of the reason for these poor results is that vitamin D in large doses may not be processed by the liver to HDL because the vitamin A cofactor is not adequately supplied in a preformed (not carotene) supplement.

I remember reading in an Adele Davis book that vitamin D from the sun needed some oil on the person’s skin in order to be absorbed properly. I have not seen that information elsewhere, but if true it would explain much of the cause of deficiency in our shower obsessed culture. Perhaps other People’s Pharmacy fans know whether there is truth to this idea?

Part of the problem might be the source of the vitamin D. My allergist told me that he would take patients off of prescription vitamin D because their levels were up, then when they took the vitamin D sold at the biggest big-box store, their levels would plummet. Obviously, there wasn’t much of the vitamin in those capsules. Supplements are not regulated and may not contain what they claim to. He told me to buy my vitamins somewhere else.

Most autoimmune diseases are caused by microscopic virus or parasites within the cell walls. So it makes sense that taking vitamin D won’t help an autoimmune problem. I had organs shutting down from autoimmune. When I found this out I took a product that could pass through cell wall and kill virus. My immune system is up and running and I don’t have autoimmune anymore.

On my doctor’s advice, I started taking 2,000 iu daily several years ago, but this winter increased it to 4,000 since flu was rampant at my workplace. My seasonal allergies are almost non-existent this spring …

Also keep in mind that vitamin D is a fat-soluble vitamin, so its absorption is enhanced by bile in the intestine. Bile is secreted in response to a meal containing some fat, so vitamin D is best absorbed after a meal that contains at least some fat (probably best after dinner). People who take vitamin D with water or juice or skim milk on an empty stomach may be absorbing very little of it.

What about vitamin D-3?

Have been supplementing with D3 with great success for several years now. Grandson who is now 13 has brought his asthma under control by taking D3 5000iu and magnesium 400 mg daily. He is doing so much better than taking the singular and he has started to grow without any major attacks. When he has an issue he drinks some Mountain Dew and very rarely he uses an inhaler. Maybe, because they were studding maga doses, and what the body dose not use it pees out is the problem. Taking a smaller dosage daily works well for our family.

I think a lower daily dose of D3 is more effective than once-a-month mega doses. I am more than 90 years old, do not get out in the sun very often, and have been taking 5000 IUs of Vitamin D3 daily. My blood test in December 2016 shows I have a normal level of D3 circulating in my blood: Vitamin D 25 Hydroxy 73.3 ng/ml within the normal range 30.0-100.0.

No mention was made either, that D3 needs to be taken in conjunction with
vitamin K2 MK7 form. Otherwise my understanding is vitamin D can contribute
to deposits of calcium in the arteries.

Low vitamin D levels are a fairly new concern. Just as we only absorb approximately 500-600 mg Calcium at a time, one should ask what is the threshold for vitamin D absorption orally and are all instructed to take with a fatty meal or snack to aid the absorption of this Fat soluble vitamin? Would taking a higher dose daily of vitamin D3 improve absorption if taken with fat? Still some questions out there about dosing and instructions provided to patients taking it – several of my co-workers have reported taking it on an empty stomach or with a no fat meal such as non fat yogurt. They were clueless to needing to take a fat soluble vitamin with fat.

My personal and professional experience informs me that Vitamin D in pill form is not absorbed, but it is absorbed when given in liquid form (i. e. drops in oil).

I’m disappointed that the article didn’t answer the question it posed in its Title. Or tell us if 5,000 mcg/units? a day helps us in any way at all?

I personally have taken Vlt. D for years and rarely get sick!! I do eat a healthy diet also. Last year, I had some red spots come up on my arm and went to a doctor to see what was wrong. She froze them off and a few months later; more popped up. I thought about it and upped my Vit. D and within a few days; spots gone!! Haven’t had any since. So, if you keep your D level up; I’m sure it helps prevent some health problems rather than waiting till you have a health problem and then expect Vit. D to cure it. Just my opinion.

I twisted the arm of my primary care Doc and was shown to be “dangerously deficient” (her words). She prescribed D2 in large dose (can’t remember exactly) but when I did a little reading and research, I found that the body needs K2 in order to absorb vit.D. So I got a sublingual tablet of D3+K2. My D level is now great. I may have missed it; was K2 discussed here???

A few years ago, one doctor I met with who is both an MD and practitioner of natural medicine, suggested I wasn’t absorbing the Vitamin D I was taking in supplement form. He had me begin a morning regimen with a protein shake that includes Vitamin K in the ingredients. And, liquid Vit D. Within 3 months, no deficiency. He told me Vitamin K helps absorption. Now, 4 years later, still no Vit D deficiency. (I do have auto-immune induced Addison’s Disease for 13+ years)

perhaps the issue (in these studies) is looking at vitamin d3 in isolation?

there is a plethora of research reflecting the importance of calcium/magnesium/vitamin d3/vitamin k balance. but, then again, balance is the key to many things.

i wouldn’t discount the importance of vitamin d3 and supplementation. and, again, there are individualized factors to take into account.

in addition, i would second michael f’s comment regarding prevention as opposed to correction.

So I still need 10 min of sunshine daily, plus I need to know how to do that in the winter, how much skin needs to be exposed.

Also, i need to research what foods meet the needs of a diet with the rda of D?

I take 10,000 iu a day. I work at night so I take it year round. Wife takes 5000 iu/day. She gets sunshine in the summer daily so she doesn’t take it then. In Việt Nam ( I visit often) go bare armed and be outside every day for a n hour or two and no supplement is needed under that tropic sun. I have some direct anecdotes in re other viruses that I won’t talk about because they are single instance but make me wish I had the resources to try it on large groups.

I’ve been taking 5,000 IU of vitamin D daily for the past 13 years. Prior to that, I would easily catch colds, and I annually caught bronchitis. No more. I’m now 54, and I haven’t been sick one single day since my vitamin D levels have been normalized. Not one single day. And I routinely am around (and even share food with) my many grandchildren — and you know how easy it is to catch bugs from little kids. (I buy them vitamin D constantly, too.) I discovered way back that my level was at 19. Now it’s consistently in the 80s. I’m a total vitamin D convert and fan, and no one could convince me otherwise!

Comments from one of your recent articles brought to my attention that the reason I have not been sick from communicable disease since 2012 is because I started taking daily vitamin D. The one time I caught something, it was very mild and only lasted a few days.

I agree with your conclusion that a daily dose is more effective. One year ago my lab work showed that my hydroxy 25 reading was 32. After one year of 5000 IU 2x per day my reading is 62 which is in an optimum range.

I hope my experience proves that doctors have forgotten that each patient is a unique individual. I knew little about medicine until I had a nervous breakdown 5 years ago. Having had epilepsy for 48 years I thought my GP and Neurologist were treating me OK until I started experiencing tingling and numbness in the hands and feet. My GP referred me to a Rheumatologist who tested for Carpal Tunnel Syndrome and Raynaud’s. Both tests proved negative but she prescribed NSAID’s for pain relief without a firm underlying diagnosis and no further investigations?

Something told me to pay privately for a Chiropractor, who promptly x-rayed the spine, found the left hand side of the vertebrae was crumbling and diagnosed Degenerative Disc Disease (Osteoarthritis). He recommended high dose Vitamin D (5000 IU’s), Vitamin B-Complex and Vitamin C, with CalMag (500 mgs each of Calcium & Magnesium) daily. Nine months later a second set of x-rays showed 2 mm of new bone growth on the vertebrae and the tingling and numbness had also disappeared. I’ve learned that the years of anticonvulsant use had depleted the body’s stores of Calcium and Vitamin D. Anticonvulsants also deplete all B vitamins. My GP’s also denied to test my Vitamin D status and I had to pay City Assays to find my level was only 34 nmols (14 ng?L). Optimal range 75 – 125 nmols or 30 – 5- ng/L. I took the result to my GP, which he asked me to leave with him so that he could contact the hospital’s biochemist for an interpretation and treatment protocol. The following day he gave me a prescription for Calceos (400 IU’s with 1200 mgs Calcium) twice daily. Having researched Dr’s Carolyn Dean, Michael Holick & John Cannell, I bought Healthy Origins Cholecalciferol taking 5000 IU’s daily, retested 3 months later to find my level had jumped to 98.6 nmols/L. I continued on 5000 IU, retested a further 3 months later to find my level only rose to 111.9 nmols. This indicated to me that I needed a maintenance of 4000 -5000 IU’s daily all year and not just the winter months between September through to March.
It’s absolutely vital that patients take a proactive role in their own healthcare. With many people working in Offices, Hospitals and factories who don’t get sun exposure, it’s no wonder that the UK has an estimated 80% of the population as vitamin D deficient?

Pretty much a worthless study. They should have done daily dosing in this study, since that is what most people do.

When I started taking regular D-3 I was 2 days into a disabling flu that was knocking people out for up to 3 weeks. The formula I had read said take 900 units for each pound of body weight all at once. Repeat next day if there is no improvement. I took it before going to bed. When I rose the flu was quite gone. My wife repeated that sequence a year later except she took it in the AM and by nightfall was fine. Daughter same. Several acquaintances who have done what I said when they were ailing had the same reaction.

On the advice of my neurologist, I have taken 5000 units of d3 per day. The major thing I notice is that I do not sunburn.

I started taking 10,000units of D3 daily 11 years ago. I used to get colds and flu several times a year because my wife was a school teacher. I have had no virus in 11 years and wife in 10 years. I have never had a flu shot. She stopped flu shots 9 years ago. Same results with my three children with varying time frames. Same with the widows at church that I got started three years ago. In addition: two of the younger folks I started on D-3 were diagnosed Bi-Polar. Both have quit taking Xanax and anti psychotics and have no trace of the Bi-Polar. A woman I know in Việt Nam was severely manic depressive. I sent her a year supply in 2010 because she was highly prone to virus infections (For cultural reasons, non-laboring females in VN get no sunshine exposure). She has had no virus since and her manic depressive episodes have gone. I talked to her husband about it right after she married and he decided she should get sun every day. She is fine, virus free, and normal with two kids.

I have been taking 5,000IU of D-3 capsules for 40 years and haven’t had a cold. Also, even if hints of a possible cold coming on I take zinc logenges for one or two days.

Even though I live in Florida and play golf and am in the pool, either one daily, I am tanned and use no sun screen my doctor suggested we (husband and I) take 5,000 IU daily, Is it a waste of money and bad for us? Ages 85 and 87.

I’ve been daily dosing for a year and noticed major improvements in my immunity. I wish I’d begun taking D sooner! How do monthly large doses stay in the body? Maybe they don’t, as the study indicates.

Here’s a non-profit at UCSD that’s doing long term studies on vitamin D. Tons of great info, you can participate in the study if you like, and the ongoing results regarding health benefits are lifesaving.

Can somebody tell me why they would give people monthly doses?

“Can somebody tell me why they would give people monthly doses?”

The theory is that the liver regulates the amount of Vitamin D in the system, and causes excess from higher daily doses to be eliminated. But if a massive dose is taken weekly or monthly, the liver is overwhelmed and the higher amount circulates in the body for a time before elimination. Many physicians accept this theory and prescribe accordingly.

The research cited in this article suggest Vitamin D cannot correct the several noted problems once they occur, which may not be the same as preventing the problems from happening.

It would be nice to get study results from a daily dose.

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