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Low Vitamin D Levels Linked to Risk of Alzheimer Disease

Older people with low vitamin D levels are more vulnerable to dementia. A new study shows that taking vitamin D may help prevent dementia.

Most vitamins must come from our food (or supplements) because we don’t make them ourselves. Vitamin D is an exception, because our skin makes the precursor to this hormone when we expose ourselves to sunlight. However, a deficiency in vitamin D is as serious as any other vitamin deficiency. The adverse health consequences of low vitamin D levels include high blood pressure, arthritis, infection, kidney disease, and osteoporosis. Studies have also linked vitamin D deficiency to immune system problems, respiratory diseases and diabetes. Some doctors monitor their patients’ vitamin D levels.

Should You Take Supplements to Correct Low Vitamin D Levels?

Q. My doctor requests a vitamin D level every time I get a blood test. A few years ago, it was lower than he wanted, so he suggested I take D3.

I am not spending as much time working outside, so my body doesn’t seem to produce as much vitamin D. I really appreciate his caution, as I haven’t even had a cold since I started on the supplement.

A. We think it makes sense to test vitamin D levels periodically. Millions of Americans are low or deficient in this crucial nutrient.

Many studies show that when people do not have adequate vitamin D, they are more susceptible to infection. A placebo-controlled trial of supplements (5,000 IU vitamin D3 daily) found that volunteers on D3 were less likely to contract influenza-like illness than those on placebo (Nutrients, Dec. 20, 2022).

Low Vitamin D Levels and the Risk for Dementia:

The immune system is not alone in its need for adequate vitamin D. People with low vitamin D levels may also have an increased risk for dementia (American Journal of Clinical Nutrition, April 22, 2022). Researchers analyzed data from 294,514 participants in the UK Biobank. Investigators had performed blood tests and neuroimaging on each of these volunteers. Volunteers entered the study between 2006 and 2010, when they were between 40 and 69 years old. Data collection continues to this day. For this analysis, median follow-up is 11 years.

The blood tests allowed scientists to determine circulating levels of 25-hydroxyvitamin D. They found that people with low levels of 25-hydroxyvitamin D were at greater risk for dementia.

How Much Vitamin D Is Enough?

The scientists suggest that the optimal levels of 25-hydroxyvitamin D may be between 25 and 50 nmols per liter. Those with low vitamin D levels (below 25 nmol/L) were half again as likely to experience a stroke or dementia as those with levels of 50 nmol/L. The analysis suggests that if everyone had 25-hydroxyvitamin D levels of 50 nmol/L, dementia diagnoses would drop by 17%. No benefit was apparent at higher blood levels.

Samples in the UK Biobank allow scientists to look for specific genes, designated SNPs. (SNP stands for single nucleotide polymorphism. They indicate genetic variation.) However, there were no obvious connections between specific gene variants and vitamin D levels or dementia.

The authors suggest that vitamin D could promote the growth and development of nerve cells. In addition, it may help protect blood vessels supplying the brain. Finally, adequate vitamin D levels may also have an anti-inflammatory effect on brain health.

To summarize, they end their report:

“In conclusion, our study supports a role of vitamin D deficiency on brain health, notably for the risk of dementia.”

Does Extra Vitamin D Ward Off Dementia?

It’s one thing to determine that low vitamin D levels increase the risk for dementia. It is quite another to demonstrate that taking extra vitamin D supplements will reduce the risk of developing dementia. But that is precisely what a group of researchers set out to discover. They have just published the results of their efforts in the journal Alzheimer’s & Dementia: Diagnosis, Assessment & Disease Monitoring, March 1, 2023.

A ten-year study of more than 12,000 older adults found that those taking vitamin D were less likely to be diagnosed with dementia during that time frame. None had such a diagnosis at the start of the study.

Those who took vitamin D, whether in combination with calcium, as D2 (ergocalciferol) or as D3 (cholecalciferol), were 40 percent less likely to develop dementia. Women and people without mild cognitive impairment at the beginning of the study got the greatest benefit from vitamin D supplementation.

The authors explain it this way:

“While exposure to vitamin D was associated with significantly lower dementia incidence in both males and females, the sex-specific difference was also statistically significant. The effect of vitamin D exposure was greater in females than males. This finding might be explained by the associations of estrogen and activated vitamin D and declining levels of estrogen in aging females. Evidence has shown that estrogen may increase the activity of the enzymes responsible for activating vitamin D. Subsequently, it can be hypothesized that declining levels of estrogen in peri- and post-menopausal stages could contribute to vitamin D deficiency in females.”

The investigators concluded that the earlier people started taking the nutrient the more likely they were to experience benefit against cognitive decline.

A Reader Using Vitamin D to Prevent Cognitive Decline:

Q. I’ve been taking 2000 IU of vitamin D3 daily for many years, along with several other supplements and vitamins. I am the oldest and last survivor of my family. My siblings all were in either memory care or assisted living when they died.

I give a lot of the credit to my vitamins, but I also have lived an active life. I’m 88, still manage all my affairs, read a lot and walk a mile or two a day, depending on the weather.

A. It sounds like you are doing everything right. Many people would like to know how to ward off dementia. Staying active both physically and mentally is a great first step.

Vitamin D may also be beneficial. As discussed above, people with low blood levels of 25-hydroxyvitamin D are at greater risk of dementia. In addition, recent research indicates that people who take vitamin D supplements are 40 percent less likely to develop dementia. People who start the supplement before they notice cognitive decline seem to get the most benefit. That description fits your situataion.

Your dose of 2000 IU/day is above the RDA for people your age (800 IU, which might also be stated as 20 mcg). However, it is comfortably below the tolerable upper limit for adults of 4000 IU (100 mcg). To learn more about the pros and cons of this supplement, you may wish to read our eGuide to Vitamin D and Optimal Health.

Vitamin D vs. Drugs for Alzheimer’s Disease?

If you have been reading our newsletter you know that there has been tremendous controversy surrounding the FDA’s approval of two new drugs for dementia. The first was Aduhelm (aducanumab).

We described an 18-month congressional investigation into the approval process at this link. In a word, it was messy! Many people, including outside experts for the FDA, raised concerns about the effectiveness of the drug.

The second drug to get FDA approval against Alzheimer’s disease was Leqembi (lecanemab). It got the green light on January 6, 2023. You can read our take on this new dementia drug at this link:

YIKES! FDA Approves Lecanemab Against Alzheimer’s

The list price for both new medications will be over $26,000 per year. And that does not include other expenses. Many patients will have to have MRI scans to make sure they are not experiencing brain swelling or other serious side effects.

More important, neither drug has been shown to dramatically reverse dementia. There is no clinical data demonstrating that either medication will prevent the onset of Alzheimer’s disease. And the drug company has not shown that these pricey new drugs will allow people to resume normal activities of daily living or delay entrance into a nursing home.

What Price Protection?

Just out of curiosity, how much do you think a year’s worth of vitamin D might cost? We often recommend the subscription service www.ConsumerLab.com for determining the best herbs and dietary supplements. Since the FDA doesn’t test for quality, we have to rely on this independent service.

ConsumerLab recommends Source Naturals Vitamin D-3 liquid drops. If you were to take 2,000 IU daily for a year, the cost would be under $20. Compare that to the cost of FDA-approved pharmaceuticals. If you would like to learn which tablets, capsules or softgels ConsumerLab.com recommends, you will have to subscribe to the service.

Earlier Studies on Low Vitamin D Levels:

The study using data from the UK Biobank was not the first to suggest a link between vitamin D and the risk of dementia. In 2010, a study followed 858 senior citizens in Italy for six years (Archives of Internal Medicine, July 13, 2010). The scientists measured blood levels of vitamin D of the participants at the beginning of the study in 1998.

The subjects took tests to measure their attention, decision making and overall cognitive ability. These occurred at the start of the study, three years into the investigation and at the end, after six years.

People with inadequate levels were 60 percent more likely to experience mental decline over the course of the study. The investigators point out that randomized, controlled trials are essential to determine whether giving older people vitamin D supplements can help reduce cognitive decline. We agree and would like to see such studies performed.

Until then, however, it seems prudent for people to assess their vitamin D levels and do what they can to normalize their values. The trouble is that studies of vitamin D supplements have not always shown that they can reliably reverse the risks of low vitamin D levels.

How to Boost Low Vitamin D Levels:

Q. My vitamin D level measures 5, which indicates deficiency. The doctor prescribed 50,000 units once a week to correct this low vitamin D level.

The pill causes me bloating, gas, constipation and acid reflux, so I am going to stop taking it. What else can I do to bring my low vitamin D level into the normal range without suffering these uncomfortable symptoms?

A. If it were spring or summer, the easiest way to boost your blood level of vitamin D would be to spend some time in the sun every day. (You wouldn’t want to get sunburned, but a few minutes a day can often do the trick.) But in winter, that tactic won’t work.

Try Changing the Dosing Schedule:

The problem might be the once-a-week regimen your doctor prescribed. Many people do well with this prescription, but others have problems. And it may not provide vitamin D in the best way for the body to use it.

One study that looked at circulating vitamin D levels concluded:

“for the optimal functioning of these systems [dependent on vitamin D], significant vitamin D should be available on a daily basis…” (Journal of Clinical Endocrinology and Metabolism, Dec., 2013).

Vitamin D is fat soluble, which is what has led doctors to embrace a once-weekly or once-monthly dose. The research cited above shows, however, that vitamin D is not stored efficiently and many people do better with a daily dose.

You might find that taking a smaller amount of vitamin D3 every day will cause less digestive distress and deliver a better result. Be sure to take the pill with a meal that contains some fat. Often the evening meal is best for maximal absorption.

You may wish to consult our eGuide to Vitamin D and Optimal Health for more details. You will find it under the Health eGuides tab.

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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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