Vitamin D: What to Know & How Much to Take

Vitamin D: What to Know & How Much to Take

Confused by all the back and forth in the media about vitamin D?

That’s understandable. Once touted as the thing to take for health and well-being, vitamin D has actually not been meeting expectations in randomized trials. It’s even been demoted in some expert recommendations.

That said, there is still a pretty easy and straightforward approach that most older adults can take.

In this post, I’ll explain what I recommend to most of my older patients, and why it’s important to be careful about taking higher doses of vitamin D3.

I’ll also address the following vitamin D frequently asked questions:

    • How much vitamin D to take every day?
    • What does vitamin D do?
    • What to know about the symptoms of vitamin D deficiency
    • The benefits and side effects of vitamin D
    • Which type of Vitamin D should I take?
    • Do I need to have my vitamin D blood level checked?
    • What should one’s vitamin D level be?
    • Will vitamin D prevent falls or fractures?
    • Will vitamin D prevent dementia, cancer, and/or premature death?
    • I am outside a lot. Do I need a vitamin D supplement?
    • I heard that a higher level of vitamin D is better for you. How much is too much?

Now, when I first wrote this article in 2015, vitamin D supplementation for older adults was recommended by experts — to help reduce the risk of falls and fractures, among other things — although most geriatrics experts did not think the high doses (e.g. 2000 IU daily or more) that many people take are indicated.

(For years now, many people have had unrealistic expectations of what vitamin D can do for them. Sometimes this is because they think it will improve their health. In other cases, it seems to be because their doctors never got around to reducing a higher dose which should’ve only been used for a limited time. Either way, it’s concerning because taking high doses of vitamin D has been linked to problems, as I explain below.)

Today, experts in geriatrics are reassessing what to recommend for vitamin D supplementation.

This reassessment is in large part driven by the publication of a large randomized trial of vitamin D supplementation in older adults, the VITAL study, plus a few other research studies that have suggested that higher doses of vitamin D supplementation are associated with more falls and hospitalizations.

The results of the VITAL study, first reported in 2019, found that vitamin D supplementation did not reduce cancer or cardiovascular disease, over a follow-up period of about 5 years.

Two follow-up studies, using data from the VITAL study, also found that vitamin D supplementation did not reduce falls, and did not reduce fractures.

VITAL was a very well-done study; it included over 25,000 participants. But, the average age was 67. Only 12% were over age 75 and most didn’t have very low vitamin D levels to begin with.

So for geriatricians like me, who mostly focus on people over age 80, many of whom have osteoporosis…VITAL is important information, but it’s also not the last word.

As of 2024, my take is that if you are over age 65, it’s ok to take a vitamin D supplement. If nothing else, the dose I suggest will almost certainly prevent vitamin D deficiency, and it will also often correct a low vitamin D level.

But, if you take vitamin D: it should be a sensible dose, you probably don’t need blood tests, and you shouldn’t expect it to work miracles.

Read on to learn how much vitamin D to take, why I recommend taking this vitamin, an overview of recent important research, plus answers to those FAQs.

My Recommended Daily Dose for Vitamin D in Older Adults

I used to recommend a supplement of vitamin D 1000 IU/day. This was the dose recommended by the American Geriatrics Society (AGS), starting in 2013. (As of 2024, they have not yet changed their recommendation.)

However, I’ve recently decided to suggest a vitamin D dose of 800 IU/day, in part because of the results of this 2021 study.

I do this because:

    • Many older adults have risk factors for vitamin D deficiency. These include having osteoporosis and spending limited time outdoors.
    • The skin becomes less able to synthesize vitamin D as people get older.
    • Vitamin D seems to be involved in muscle function. Early research suggested it can help reduce falls. Although more recent research hasn’t confirmed this finding, either way, it seems sensible to avoid frank deficiency (meaning, levels lower than 20 ng/mL).
    • In the vast majority of older people, taking vitamin D 800 IU as a supplement every day has a low risk of side effects.
    • Research suggests that taking vitamin D 800-1000 IU/day will prevent low vitamin D levels in most older adults.


Other expert groups have provided similar vitamin D guidance. For instance, in 2010 the Institute of Medicine (now the National Academy of Medicine) published a report with age-based Recommended Daily Allowances for vitamin D in “normal healthy persons.” For people aged 1-70, they recommended 600 IU/day. For people aged 71+, they recommended 800 IU/day.

Research suggests that low levels of vitamin D are common in older adults who don’t take supplements, but are uncommon in those who do take supplemental vitamin D.

I think 800 IU/day of Vitamin D is reasonable. I call this the “healthy aging” dose of daily vitamin D.

For people who are already taking a multivitamin or calcium supplement, should check to see how much vitamin D is already included, as they may already be getting 800 IU from those supplements.

Are you wondering about taking a higher vitamin D dose? See the section below on vitamin D side effects.)

The basics of Vitamin D

What is Vitamin D and what does it do?

Vitamin D is a fat-soluble vitamin that can be synthesized by the skin in response to sun exposure. It’s also naturally present in certain foods (mainly fatty fish such as salmon or mackerel) and is commonly added as a supplement to certain foods (milk, breakfast cereals).

In the human body, vitamin D plays a key role in calcium metabolism and in bone health. Vitamin D helps the gut absorb calcium and helps regulate blood levels of calcium and phosphorus. (Calcium and phosphorus are mineralized in the body to create and maintain bones.)

Vitamin D also appears to play a role in many other parts of the body, with most tissues of the body having vitamin D receptors. It is thought to be involved in managing the immune system, inflammation, cell growth, muscle function, and more. Research is still ongoing to better understand just how vitamin D affects health and disease.

Vitamin D in aging: As we age, we generally retain the ability to absorb vitamin D in our guts, but our ability to synthesize it in the skin goes down. This, in combination with less time outside, is why low levels of vitamin D are thought to become more common in later life.

What are the symptoms of vitamin D deficiency?

The symptoms of vitamin D deficiency depend on how severe the deficiency is, and the age of the person.

Originally, vitamin D deficiency was identified as the cause of a bone problem in children called rickets. This type of deficiency mostly occurs in malnourished children growing up in impoverished settings; it’s rare in the U.S.

However, in the early 2000s, some health providers began noticing that some adults have low levels of vitamin D. Many people with lower levels of vitamin D have no physical symptoms, even if their levels of calcium and phosphorus are abnormal.

However, in some people, very low levels of vitamin D might be associated with symptoms, such as bone pain, fractures, muscle weakness, and difficulty walking.

Laboratory symptoms of vitamin D deficiency: If vitamin D is low enough to affect calcium and bone metabolism, this can result in abnormal blood tests. Along with a low level of vitamin D, one might find abnormally low blood levels of calcium and phosphorus, and possibly abnormally high levels of alkaline phosphatase (an enzyme in the body) and parathyroid hormone.

What are the benefits of vitamin D supplements?

This has been hotly, hotly debated. Several observational studies done in the 2000s found an association between low vitamin D levels and all kinds of bad health outcomes. There were also associations between higher vitamin D levels and good health outcomes.

This led many people to conclude that more vitamin D supplementation would improve health outcomes (e.g. fewer falls, fewer fractures, less cancer, longer lives, etc).

However, since those initial years of excitement about vitamin D, several large randomized trials have been completed. Unfortunately, these mostly have not found any particular benefits to higher levels of vitamin D supplementation. Key vitamin D research includes:

Per this comprehensive review of vitamin D research done in older adults, it seems that vitamin D supplementation is most likely to benefit those who have a severe deficiency. Whereas supplementing people who have only mild deficiency (or no deficiency) does not generally lead to any benefits.

What are the side effects of vitamin D supplements?

People generally don’t notice any symptoms or side effects from taking vitamin D, whether they are taking a dose of 800 IU per day (my recommended dose) or a dose of 50,000 IU per week (that’s a higher dose that is sometimes prescribed to help treat a vitamin D deficiency and bring blood levels to normal more quickly).

However, randomized studies of vitamin D supplements in older adults have found that higher doses are associated with a higher chance of falls and fractures. (See here, here, and here.)

There is also this 2019 randomized trial that found that vitamin D doses of 4000 IU/day and 10000 IU/day resulted in lower bone mineral density, compared to 400 IU/day.

All of this means that at this point, we have several randomized studies finding some worrisome side effects when older adults take higher doses of vitamin D (e.g. 2000 IU and higher), whereas doses lower than 1000 IU/day seem to be safer.

For this reason, I believe older adults should not chronically take high doses of vitamin D unless they are under medical supervision and there is a particular reason to do so.

For more on the research on vitamin D in older adults, see this 2022 review article: Vitamin D in the older population: a consensus statement.

Frequently Asked Questions about Vitamin D

Which type of Vitamin D should I take? 

Most supplements contain vitamin D3, also known as cholecalciferol. Studies suggest that this increases blood levels a little better than vitamin D2 (ergocalciferol).

Both these versions of vitamin D require processing by the liver and kidneys. People with liver or kidney disease may need to get a special type of supplement from their doctors.

Although Vitamin D supplements are usually taken daily, they also come in higher doses, which may be prescribed for weekly or even monthly dosing. (These are available over-the-counter, but I think it’s best to take these under medical supervision.)

I recommend a daily dose of vitamin D3 800 IU/day.

Do I need to have my vitamin D blood level checked?

Probably not. The AGS consensus statement says that testing vitamin D levels should be unnecessary in most older adults, unless some particular symptom or disease warrants it.

(I’m not aware of any research published in the past few years that makes a case for routinely testing vitamin D levels of older adults.)

The idea is that if people take a daily vitamin D supplement as recommended above, they’ll be highly unlikely to have a vitamin D level that is too low or too high.

On the other hand, if you have been diagnosed with a serious vitamin D deficiency, your doctor will likely recommend a higher dose of vitamin D supplementation. In this case, most experts recommend a repeat vitamin D blood test after 3-4 months of treatment. For most people, the test would be for the 25(OH)D level. People with certain conditions may require a different type of test.

I do end up checking vitamin D levels sometimes in my practice, because many of my patients have severe osteoporosis, or sometimes an abnormal blood calcium level.

I find that when I check vitamin D in an older patient who is not taking a supplement, they often have a low level. Probably there are some elderly farmers out there who get enough sun to maintain a good level without taking a supplement. But it seems fairly common for older adults who don’t take a supplement to have low levels.

That said, I agree with those who say that vitamin D testing is often overused. But of all the tests and services to overuse, this one strikes me as fairly minor. If you’re worried about overtesting or overtreatment, it’s far more worthwhile to avoid unnecessary scans, procedures, and medications.

What should one’s vitamin D level be?

This question has been hotly, hotly debated. At this time, it depends on whom you ask.

The Institute of Medicine believes a blood level of 20-40 ng/mL should be adequate. The Endocrine Society, the American Geriatrics Society, and some other expert groups recommend a level of at least 30 ng/mL.

(Note: in US laboratories, vitamin D levels are usually reported in ng/mL. In other countries, they are often reported in nmol/L. You can convert between units here.)

As noted above, the party line — which I consider reasonable — is that most people don’t need their vitamin D level checked. In the absence of certain health problems, a low vitamin D level is unlikely in someone who takes a daily supplement.

Research suggests that vitamin D supplementation is most beneficial to people who start with a vitamin D level of less than 20 ng/mL (equivalent to 50 nmol/L).

Will vitamin D prevent falls or fractures?

Unclear. For the average older person in reasonable health who starts off with a vitamin D level of 20ng/mL, probably not!

Some studies several years ago suggested that vitamin D reduces the chance of these serious health events, but these results have been questioned by later studies.

Plus, these two studies based on the large well-done VITAL study were negative:

The US Preventive Services Task Force recommends Vitamin D to help reduce fall risk. But in 2018, they changed their recommendation. (They also said that their new recommendation doesn’t apply to people with osteoporosis or vitamin D deficiency.)

My current take is that it’s still possible that vitamin D might help with fracture risk, especially for certain older adults with osteoporosis. Since a dose of 800 IU/day has a low chance of harm and possibly helps some people a least a little, I recommend it.

However, I usually tell people to not have overly optimistic expectations of vitamin D’s effects. In most older adults, problems such as pain, fatigue, and/or falls are due to multiple underlying causes, so there’s often no easy fix available.

Will vitamin D prevent dementia, cancer, and/or premature death?

Several studies have identified an association between vitamin D deficiency and diagnoses such as Alzheimer’s disease and cancer. In other words, people with these conditions tend to have low vitamin D blood levels.

But an association isn’t the same thing as causation, so it’s not yet known whether vitamin D deficiency causes these diseases. It’s also not yet known whether taking vitamin D supplements will reduce one’s chance of developing these diseases.

To date, most randomized studies of vitamin D to improve health outcomes have been negative. (Meaning, the group receiving vitamin D supplementation did not appear to do better.)

Although it’s possible that low vitamin D levels might be a factor in developing certain diseases, it’s probably a small effect. Cancer and Alzheimer’s, after all, generally seem to be the result of lots of little factors — genetics, epigenetics, stress, immune function, nutrition, inflammation, toxins — interacting over time.

In 2010, the Institute of Medicine concluded: “This thorough review found that information about the health benefits of vitamin D supplementation beyond bone health—benefits often reported in the media—were from studies that provided often mixed and inconclusive results and could not be considered reliable.”

Subsequently, the VITAL study — which randomized 25,000 adults over the age of 50 to take vitamin D supplements (2000 IU/day), omega-3 fatty acides, both, or neither for 5 years — found that neither intervention was effective for preventing cancer or cardiovascular disease: Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease (NEJM, Jan 2019).

A similarly large randomized trial based in Australia, which included 21,000 people aged 60 and older, found that vitamin D supplementation was not associated with decreased mortality; at 6 years, overall mortality was 5% in each group.

My take: although the ongoing research on vitamin D is very interesting, it’s unlikely to make practical changes to my current approach.

A daily dose of vitamin D 800 IU should prevent very low vitamin D levels, and should be sufficient to help most aging adults get the benefit — whatever it may be — of vitamin D.  Furthermore, vitamin D 800 IU/day seems unlikely to cause harm to most older adults.

Over the past ten years, no research I’ve heard of has indicated that I need to change this approach.

The bottom line is this: Avoiding low vitamin D levels is probably beneficial to health, but there’s no solid evidence suggesting that high vitamin D levels are particularly beneficial to health. And there is definitely accumulating evidence from randomized trials that higher doses of vitamin D3 supplementation are associated with worse outcomes.

I am outside a lot. Do I need a vitamin D supplement?

Hard to say without checking your levels. In general, I recommend people take a daily vitamin D supplement no matter how much time they spend outside.

To begin with, it’s usually a good idea to wear sunscreen if you are going to be exposed to UV radiation, because skin cancer is very common!

Also, for your skin to synthesize vitamin D, you need to be exposed to UVB radiation. This type of solar radiation gets scattered by the atmosphere, so exposure will be affected by season, latitude, and the time of day. (You probably won’t get much UVB radiation to synthesize vitamin D if you are out in the early morning or later afternoon.)

Furthermore, even if you are getting enough vitamin D through sunlight or diet, taking a supplement of 800 IU is unlikely to raise your vitamin D levels to a problematic range.

In my view, people of all ages usually have plenty they can and should do for their health and their lives. Is it really a good use of your valuable time to spend it figuring out how much vitamin D you might be getting through sunlight and/or your food?

I say it’s better for you to take whatever vitamin D supplement is recommended for your age (or by your doctor), and focus your energies on getting enough exercise, implementing other healthy habits, taking care of those who need you, and managing any chronic conditions you have.

I’ve heard that a higher level of vitamin D is better for you. How much is too much?

This is being actively studied, and actually, in recent years, several randomized trials have been published that suggest higher levels of vitamin D (e.g. over 40 ng/mL) might be associated with worse health outcomes in older adults.

For instance, the STURDY trial, published in 2022, concluded that “the risk of consequential falls may be increased with achieved concentrations ≥ 40 ng/mL.”

Another trial, which was a randomized trial of 4 different doses of vitamin D in older adults, concluded that their analyses raise safety concerns about higher doses.

When the American Geriatrics Society issued their recommendations in 2013, they said that most people, total vitamin D (from supplements and food) shouldn’t exceed 4000 IU/day.

But given the more recent research, I am now advising against doses higher than 1000 IU/day, unless a severe documented deficiency is being treated under close medical supervision.

Research into the risks of too much vitamin D is ongoing. A study of very high vitamin D supplementation (500,000 IU once a year) increased falls and fractures in older adults, so clearly it’s possible to have too much of a good thing.

Vitamin D also promotes calcium absorption, and high levels of vitamin D can cause high levels of blood calcium.

I have also personally encountered a few patients with high blood calcium levels, who were taking high doses of vitamin D supplements and had fairly high blood levels of vitamin D.  One of them went on to have a heart attack a few months later; his blood level of vitamin D had been about 70 ng/mL. This is a single case, but some research does suggest that high levels of vitamin D may be associated with coronary artery calcifications, especially in men. It is certainly possible that future research may find links between high vitamin D blood levels and increased heart attack risk.

My own practice now is to caution patients if they are taking daily vitamin D supplements of more than 1000 IU/day in the absence of documented deficiency. I also discuss a reduction in vitamin D supplementation if a patient has a blood level greater than 50 ng/mL.

I know that some health providers recommend substantially higher vitamin D levels, but as best I can tell, there is no high-quality research evidence to support this, whereas there is increasing evidence that high levels and/or high doses have risks.

The bottom line on Vitamin D3 supplements

The bottom line on vitamin D is this: it’s good to avoid very low levels by taking a daily dose of 800 IU/day. However you should be careful about taking more than 1000 IU/day because multiple randomized trials are noticing worse outcomes in participants randomized to higher doses of vitamin D.

And you probably don’t need to have your vitamin D levels tested (unless you have bad osteoporosis or a recent fracture).

So take a daily supplement of 800 IU. But ask questions if your doctors want to test you, especially if you’ve already been taking vitamin D supplements.

And if for some reason you are taking a higher dose of vitamin D — such as 50,000 IU per week — be careful about continuing it indefinitely.  For most people, higher doses should only be used for a few months, and then a lower maintenance dose should be possible.

This article was first published in Jan 2015. It received a major update by Dr. Kernisan in June 2024. 

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