Vitamin D and physical function: Is more better?

Robert H. Shmerling, MD
Robert H. Shmerling, MD, Faculty Editor, Harvard Health Publications

The popularity of vitamin D has been surging in recent years, largely because of the growing list of its proposed health benefits. But not all of the claims are backed by evidence. For example, there have been suggestions that vitamin D can help you

  • reduce your risk of arthritis
  • prevent heart disease
  • improve your brain function and lessen your risk of dementia
  • improve your immune function and lessen the risk of immune disorders.

These are difficult claims to prove — or disprove. Most of them come from studies linking a low intake of vitamin D or a low level in the blood with an increased risk of disease or death. But, it’s possible that people with low intake or blood levels of vitamin D levels also smoke more, exercise less, or have other explanations for their higher rates of disease and death.

While it’s not at all clear that vitamin D can deliver these health benefits, getting enough vitamin D is important, especially for maintaining bone health. Severe deficiency of vitamin D can cause osteomalacia, which means “soft bones.” (In children, abnormal bone development due to vitamin D deficiency is called rickets.) Low levels of vitamin D can also contribute to osteoporosis: vitamin D is needed to promote calcium absorption in the gut, and calcium is essential in building and remodeling bone.

Can vitamin D also improve physical function?

To explore the possibility that vitamin D might provide yet another health benefit, researchers recently published a study to determine whether taking a high dose vitamin D supplement might help stave off a decline in physical function in older adults. Researchers enrolled 200 people who were at least age 70 and who had reported a fall in the past. Some were given a low dose of vitamin D, while others received higher doses. After a year, the researchers assessed the participants’ physical function (by measures of walking speed, ability to stand up repeatedly from a sitting position, and balance). The results were no better in those treated with higher doses of vitamin D than in those on lower doses. In addition, those receiving the higher doses reported significantly more falls. There was no clear explanation for this unexpected finding.

While this study casts doubt on vitamin D as a panacea for failing physical function among elderly adults, it’s still possible that it might help certain people — for example, perhaps younger adults who’ve never fallen before would see more benefit. Or, a longer period of follow-up might reveal other benefits associated with taking high-dose vitamin D supplements.

Please stand by

While we know vitamin D is an essential part of a healthy diet and supplements might be helpful for those who don’t get enough, we need more research to back up some of its proposed benefits. In the meantime, it seems reasonable to choose a balanced diet that contains the recommended daily amount of vitamin D for your age and gender. Sun exposure (perhaps as little as 10-15 minutes a day) may also increase blood levels of vitamin D because UVB radiation from the sun converts precursors of vitamin D in the skin.

Talk to your doctor about whether to have a blood test to confirm that you’re getting enough vitamin D. And read the reports about the health benefits of this vitamin (and other vitamins and supplements) with a skeptical eye. There is considerable uncertainty about what vitamin D can do for you — and, as demonstrated in this latest research, one thing is clear: more is not always better.


  1. JoAnn

    Just something that may be of interest: I am a 56 year old woman who avoids the sun due to concern about wrinkles and other sun related skin damage. I had severe pain all over my body and was diagnosed after a number of tests and various MD visits, with fibromyalgia. My serum vitamin D level was 20 ng/mL at that time. I started taking 2000 IU vitamin D supplement daily and over time, my serum level increased to 89 ng/mL. My fibro symptoms were gone. My physician expressed concern over my “high” serum D levels, so I decreased my supplement from 2000 IU per day to 1000 IU per day. My fibro symptoms returned. Without any changes in my diet or lifestyle, I increased my vitamin D supplements back to 2000 IU per day and my fibro symptoms are gone again. My plan is to continue taking the 2000 IU, but manage my levels to remain below 150 ng/mL, a level suggested as safe by some literature.

  2. Diane E Wallis, MD

    There are too many variables in solar exposure to UV-B , and the “10-15 minutes of sunshine a day” should be abandoned as a therapeutic option. For example, solar absorption is markedly reduced in women over the age of 50 and in men over the age of 70 . Washing the exposed area within 24-48 hours will decrease the effectiveness of solar conversion to previtamin D3. Skin barriers such as window glass, makeup or skin creams will block solar absorption.n UV-B absorption is affected by latitude, time of day, time of year.

    • James A. Boatright

      Per personal communication with researcher, Dr. Michael Hollick, they could find no evidence that vitamin D synthesis could occur on the surface of the skin. The necessary precursors are not there. The UV-B radiation penetrates the epidermis to the region where it can occur. The old accepted idea that washing after sun exposure could decrease vitamin D absorption has been investigated and disproved.

  3. Apurba Prosad Basu

    I have taken Vitamin D3- 60k as advised by my doctor, as specified : 1st two months weekly one capsule , there after one capsule biweekly for two months and then one capsule per month for 3 months – for old injury ( 35 yrs back) in left foot metatarsal, suddenly causing pain and swelling after a long gap . I am 77 yrs ( wt. 62 kg) but of general health, tall, and fit and walk daily average 2 miles . I am cured now .
    But the metatarsal uneasiness reappears at intervals.
    My question is, – Can I repeat the D3 dose after few months ?
    A lot of confusion on this is there. Requested an answer.

  4. Pradip shah

    Great about vitamin D. Are we really positive of what is missing in our on body .Alot apart from one cure to another one and at the end of the day it’s the same.
    Food with the latest technology has caused us all this problem. Different fertiliser mixed with different chemical causes the most effect of all.
    I am a diabetic patient and been advice to have 20minutes of sun light for better mentioned.
    Pradip shah

  5. James A. Boatright

    I have been following this vitamin D issue in particular for several years. I have seen many “vitamin D studies” that were purposely designed to fail so that the media could trumpet the news; “Don’t believe those quack pushers of nutrition as preventive of curative for diseases. Trust your MD. He has a pill for anything.” The studies are sometimes sabotaged by giving “high doses” that are ridiculously inadequate, sometimes by simply failing to measure the serum 25(OH)D levels of the test subjects (all groups, before and after supplementation), sometimes by giving massive doses monthly “to assure compliance” instead of the daily supplementation dosage which would be required to demonstrate an autocrinal effect (basically every benefit beyond calcium metabolism and bone health). General improvement in public health achieved via inexpensive non-prescription means would financially devastate the medical establishment (which apparently includes Harvard). A healthy scientific skepticism would be one thing if the science were free to investigate and report, but preventing access to new knowledge for profit is immoral.

  6. A. Kahn

    I don’t know if any research has been done but as a doctor I noticed that Asians who have migrated to Canada are at a high risk of contracting cancers. (especially leukemias) I have seen it in relatives and with a little inquiry from people with relative or friends found this to be a common feature. Maybe less exposure to the sun plus dark skin tan most probably causes low vit. D levels in their blood. Maybe the sudden drop in their serum vit. D level might be a triggering factor??
    so I usually tell people in upper hemisphere from this part of the world to increase intake of vit.D.

  7. Michael Meszaros

    There seems to be some evidence that maintaining a level of vitamin D above 120 is useful in controlling or slowing down prostate cancer. Taking 4000 iu per day has raised my level from 84 to 134 in 2.5 months. The max recommended level seems to be 250, which makes this mid range and not unreasonable.

    • James A. Boatright

      Please note carefully that many times serum 25(OH)D levels are given in nano moles per milliliter (nm/ml) instead of the more commonly used nano grams per milliliter (ng/ml). For vitamin D, there are about 0.4 grams per mole, so those nm/ml values are 2.5 times greater than the same level expressed in ng/ml. We should standardize on reporting in ng/ml to avoid unnecessary confusion.

      • Eugene

        For vitamin D, there are about 400 grams per mole, so those nm/l values are 2.5 times greater than the same level expressed in ng/ml.

      • James A. Boatright

        Thanks for the correction Eugene. I did not bother to check my statement. However, I wish the units could be standardized to prevent confusing laymen such as I.

    • JohnOh

      Vitamin K2 appears to be additional help with Vitamin D.
      Dont confuse it with Vitamin K, a blood thickener and given to babies at birth to prevent a serious disease called hemorrhagic disease of the newborn.

      New evidence, however, is said to confirm that vitamin K2’s role in the body extends far beyond blood clotting to include protecting us from heart disease, ensuring healthy skin, forming strong bones, promoting brain function, supporting growth and development and helping to prevent cancer. While these claims about K2 appear to be very beneficial, we need to be aware many such claims are made about vitamins. Lets hope they are right. I’m off to get some.

      • James A. Boatright

        I too have read that vitamin K2, along with magnesium, seem to be an important co-factors with vitamin D in calcium metabolism. I take about 300 mcg of K2 (MK-7) along with my daily vitamin D3 supplementation. I know of no serum test for vitamin K2 level, and no tolerable upper limit has been set for K2 supplementation.

  8. Jeffrey M, Taiwan

    Dr. Shmerling, Thank you for your article. To begin with, calling D a vitamin is a bit of a misnomer; from my understanding it acts more like a hormone in the body. In this respect it is more akin to a facilitator for reactions involving other vitamins and minerals, and it would not be expected to generate results on its own. While it is true that many sufferers of say arthritis show low levels of D, this may not well be causal. Inflammation response in the body may be also tied to deficiencies in other key vitamins and minerals, although D may be important in the ability of the body to utilize those other vitamins and minerals. So simply upping levels of D alone might not be sufficient. Having said that, there is a fairly large body of evidence that D deficiency, causal or not, shows up in sufferers of virtually every major chronic disease that plagues us, from cancer and heart disease to diabetes and arthritis. Such findings would suggest a strong value to supplementation with D, given the relatively low cost of supplementation, and almost complete lack of downside, as long as one doesn’t supplement to toxic levels which are quite hard to reach. Obviously, getting sun is the best option, which is what our ancestors did for hundreds of thousands of years. It is only in the past century or less that our lifestyles have moved virtually and exclusively indoors.

    Also, regarding the study suggesting increased falls from higher levels of D supplementation, I am skeptical. For one, there is no way to explain the mechanism by which D would make people more susceptible to falls. How rigorous that particular study was remains to be seen, but there are other studies that show vitamin D insufficiency decreases muscle strength and increases the risk for falls. (Norman AW, Bouillon R, Whiting SJ, Vieth R, Lips P. 13th Workshop consensus for vitamin D nutritional guidelines. J Steroid Biochem Mol Biol 2007;103:204–5. CrossRefMedline). Frequency of falls aside, D plays a crucial role in bone health, and proper supplementation with D in addition to bioavailable calcium, and K2, which is crucial to calcium metabolism, would certainly be protective in the event of a fall.

    • James A. Boatright

      We apparently evolved with a serum level of about 65 ng/ml in a trans-equatorial environment. We should all strive to maintain that level today by whatever means necessary for optimal health. One who is concerned with preventing or curing a medical condition should cycle up to twice this level for a month or so duration a few times each year. Just my non-medical opinion.

    • Lynn

      Jeffrey, I agree with your thoughtful post, especially the fact that Vit D supplements must be augmented by Vit K-2, I also add Vit K-7 after reading about the success of increased bone mass on Bone Density exams. I have decided it was too risky and expensive for me to treat my moderately severe osteoporosis with injections that are currently available–the only remedy my endocrinologist offered of course. So far I have been very disappointed in the new slant the Harvard Medical has taken in order to promote the purchase of their printed materials. The public is certainly getting short changed with the quality of info available online, even from the CDC and NIH.

      • Lynn

        A humble correction to my post re Vit K-2: I take Vit K-2–both the MK-4 and the MK-& varieties to promote that optimum amount of Vit D and Calcium are directed toward bone mass increase rather than excretion through the kidneys. I use one supplement by Innovix Labs that contains both (MK 4 and 7) , but supplement that with an additional 100 mcg MK-7 tablet from NOW Labs to get the recommended 200 mcg’s daily total. 500-600 mcgs of MK-4 type Vit K was recommended for optimal bone mass increase. These are purchased on Amazon. This not recommended by my medical doctor, but learned from Orientals that are using this method successfully to raise their calcium levels which resulted in bone mass increase for treating osteoporosis via lab work and bone density follow ups.

      • Jeffrey M, Taiwan

        Hi Lynn, There has been research out of Japan showing that women in the parts of the country that eat large amounts of natto, the highest naturally occurring source of K2, have substantially lower incidences of hip fracture. Reversing osteoporosis is a bit more tricky than preventing it, but it can be done. For one, you may need to consider therapeutic, rather than maintenance doses of D and K2. In addition, the stimulation of bone mass through exercise is also key. I have no idea of your level of mobility, but rebounders (essentially mini-trampolines) are a very good option as they are low impact, but provide the necessary stimulus for bone growth. They can be purchased on Amazon. If financially feasible, another thing you might consider is a PEMF unit. They are approved by the FDA for bone healing, but also can play a very important role in bone health. In addition, it will boost your overall metabolism and cell health, which will benefit you in many ways beyond just bone growth. Good luck!

  9. Cal scott

    I take 5000 mg daily and this takes me to the daily level

  10. Jerry Amos

    The body generates Vitamin D3 in the skin with sunlight (here in New Hampshire in the Winter??). For some reason many researchers and the FDA push Vitamin D2 in spite of medical journal articles reporting ineffective results with D2 and distinctly better results with D3. There are reports that the body can convert some of the D2 to D3 at too slow a rate to be effective.

  11. Ernestine S Cohn

    The article did not state the form of Vitamin D (D2 or D3). I was taking 50K units of D2 for a long time and it did nothing to improve my blood level. I now take 5K units of D3 per day and I am in the mid range of .normal. Thus the article has no meaning.

    • James A. Boatright

      Until recent times, they used plant-derived D2 because that was the only “approved” form. Now that the human form, vitamin D3, is readily available, they use D2 so that the “gold standard” double blind, placebo controlled studies will fail to show any benefit.

  12. Kathleen

    It does not say if the people over 70 years of age had normal , deficient or too high levels before the study started. What level of vitamin d did the test subjects have before the study started?

    • James A. Boatright

      That’s because they carefully avoided measuring the serum 25(OH)D3 levels throughout the study as any normal person would.

  13. David E. Gleason

    After 8 surgeries for skin cancer, I can’t afford to “spend more time in the sun.” And I can’t drink milk. I eat fish as often a twice a week. but with a recommended intake of 600 IUs per day, I’d have to up that to twice a *day.* So I can’t think of a single reason *not* to recommend taking daily Vitamin D supplements, even if a direct correlation has not yet been proved. It seems negligent to suggest otherwise.

  14. Peggy Heppelmann

    Few foods other than fatty fish have vitamin D unless it is added as in milk and orange juice (which is not different than taking a supplement), so you can’t count on getting enough vitamin D from a balanced diet. The best way to get vitamin D is to spend time every day in the sun with skin exposed without sunscreen, but if you happen to have an indoor day job, or live in the north, that might not be possible, in which case supplements are the best alternative. In that case the best option is to take a daily supplement rather than monthly mega doses.

    • Lynn

      Also it should be noted that sun exposure in the northern hemisphere above the Florida line is said to be inadequate to initiate enough production by exposure of skin. The angle of the sun is not the same as in the southern hemisphere so Supplementation is needed.

  15. Elena Jane Latici

    What is the point of writing a piece about high vs low doses of ANYTHING if no indication is given as to what those doses would be. Really helpful article. Not.

  16. Steven D.

    For those who cannot absorb or tolerate oral supplements there is a natural option for getting Vitamin D when there is no sunshine, or perhaps one just cannot get outdoors, it’s called The Vitamin D Lamp, model D/UV-F. It is FDA tested and cleared, and proven effective. The Vitamin D Lamp is made in the USA by Sperti and is available online without a prescription.

  17. Ed

    Ask your Doctor? Not many doctors are up to date with the benefits of D3 and certainly were not taught much as to anything other than the drugs dealt by BigPharma. It is basically up to the individual to determine his own health and eat nourishment and take supplements as best derived and determined by self.

  18. Marcus Love

    What about sun exposure? Also, is there a more or less dose of vitamin D for those with darker skin?

    • James A. Boatright

      Dose responses to vitamin D supplementation varies between individuals, primarily with your initial serum level of 25(OH)D. Just about every one can make up to 20,000 IU of vitamin D per day with the correct amount of sun (or Sperti lamp) exposure. The required amount of UV-B exposure does increase significantly for those with darker skin pigmentation.

  19. alxzba

    PLEASE: for a health oriented newsletter, you need to educate yourself on communication in print. DO NOT use blue on white — or any other pastel color if your intent is to have your subscribers read what you send and be comfortable in doing so. You don’t need an MD to know this —- just common sense, knowing something about the physiology of vision and 5 minutes looking at a color wheel — USE COLORS OPPOSITE EACH OTHER. Please.

  20. Dr Colin Walsh

    The study which failed to show benefit used MONTHLY dosing of vitamin D. Daily dosing would have been more logical. Most of the extra-skeletal benefits of vitamin D may depend on achieving adequate blood levels of the parent compound (vitamin D3), which has a much shorter half-life than 25-OH D (the form of the vitamin usually measured in blood tests) and is more available to the body’s tissues by virtue of being less tightly bound to a carrier protein.

    • Greg Bell

      Thank you for clarifying the study and for your accurate analysis of vitamin D3 and its use through a daily doseage regime rather than some monthly dose. I would also like to add that for those that believe we receive all of our necessary vitamins and minerals through a healthy diet of vegetables, fruit and protein, I would like to point out that our produce has a fraction of the nutritional value of that which was produced decades ago.

      • donna bennett

        I am on vitamin d twice a day. I used to work outside and felt probably enough altho have osteopenia. I exercised etc. now I am on a feeding peg and I take 2 a day. I am sure my bones are soft. they call is ostepina now but not reach good and I am getting arthritis in my right hand due to feeding by bolus and lifting with that hand and grinding pills . I am trying to get off the feeding peg so I feel the vitamin d is important the formula they have me on gives me some vitamins but the herbalist today said the formula is like sugar filter water with corn syrup which I cant tolerate sugar but it seems to show my bloodwork ok with all vitamins. by b level was to high with taking b along with the crap I am taking. I am listening more with a gut feeling and I think the herbalist is more knowledgeable than any dr. I have been 1 1/2 yr with no help but a few surgeries that really did nothing and then the homeopathic is not paid at duke so I got ripped off there for a few recipes thatdont work down the tube.

      • Jane

        Yes, this is sooooo true. Fruits and vegetables do not even taste the same as they did when we ate from my father’s garden in 1940…. and butter and milk tasted better then.

      • Lynn

        The quality of our food chain has been seriously diminished in the name of producing larger, fatter cattle in a shorter time frame (grain fed rather than grass fed), you can see the difference in the color of the fat (pale and whitish rather than a healthy yellow color from grass diet and good nutrients) but also the texture. And pumping hormones into chickens through their feed to promote fast growth & increase production is common now though they try to cover it up. Chickens are bathed in a solution of bleach during processing to kill bacteria before packaging. The texture and taste (and perhaps the nutritional quality) are seriously altered. It’s rare to find a chicken that actually tastes like the ones I used to eat that were farm raised and available in grocery stores. We must take supplements or else eat truckloads of food per day to realize what our bodies need daily in vitamins, minerals and amino acids.

  21. Ted

    How can it be that there is no mention here of the connection between vitamin D and cancer? I have read in, e.g., the New York Times that the incidence of certain common cancers is significantly lower in the Sun Belt states than in the cloudier north. I had thought that this striking contrast was one of the principal reasons for the recently heightened focus on the health benefits of vitamin D.

    • James A. Boatright

      Cut, poison, and burn cancer tumor treatment is a billion dollar industry. If you could get better results by eating a high fat, low carbohydrate diet and taking lots of cheap vitamin and mineral supplements, do you really think they would agree with that?

    • Lynn

      Ted, I find that very perplexing too, especially coming from “Harvard Medical” who used to be at the forefront of all cancer prevention modalities in addition to treatments. The article here was seriously flawed, the group of 200 ill defined subjects was totally insignificant as was the basic criteria they used as others have also mentioned. Everything I read now is directed toward big pharma by the end of any article. Clinics that can truly help patients by using a team approach, ie Cleveland Clinic, are extremely cost prohibitive–requiring private pay. Their email newsletter is all about generating funds to gain tidbits of information from average citizens with larger than average medical needs. I recently wrote to this Harvard group re the money-driven article and received a “meh” response. I learn much more by reading the comments section. Thank you all.

  22. A Goldstein

    Nutrition researchers need a better understanding of individual nutrition requirements that are affected by lifestyle, diet and genetic makeup. Consumers need to ask themselves why THEY think they need nutritional supplements. Is it to compensate for poor diets (bad idea) claims from dubious websites (also bad idea) or credible resources like Harvard Health, etc. And then there is the world of plant-based supplements which can cost a lot more than the extra money spent buying healthy foods in the first place. A healthy diet provides most if not all of the putative benefits from unregulated, highly processed supplements with their questionable potency, purity and stability.

    • James A. Boatright

      Whatever you eat, do not drink the Koolaid.

    • Lynn

      The problem here is with “buying healthy food”. It’s simply too difficult for the average citizen living in urban areas of the US to obtain a healthy compliment of nutrients from the daily foods that are available w/o eating a truck load daily. Foods are: grown in nutrient depleted soils, genetically altered, over sprayed with chemicals, etc. . Animals and poultry are fed unhealthy diets to promote fast growth to feed the masses. Average to poor income level people simply cannot afford all organic, grass fed, free range, hormone free, air-cooled (rather than cold bleach bath), etc. etc. foods. That is why Supplements are needed by most. Personal health needs and ancestry should also be taken into consideration. I.E., my Arian light skinned northern European ancestors did not have high vit D levels due to lack of direct angled sunlight. There was a long history of cancer, osteoporosis and other autoimmune conditions in my ancestors. I took many steps to change that in my health. Despite 25+ years of Calcium + Vit D supplements, I now have osteoporosis because the medical community did not educate me about the need for larger doses of Vit D supplementation until 15 years ago, but never that certain types of Vit K was also needed to aid the conversion of Vit D in the body. So, damage has occurred. Also my underactive thyroid was not addressed, even scorned by several physicians for years until I could no longer function, and osteopenia had begun. Then everyone was suddenly interested and I was given doses far too large for over 20 years because everyone interpreted differently or incorrectly. More damage occurred. Now through self education I’ve discovered that Vit D will not work optimally if Vit K (M-4 and M-7 types) is not adequate. But my osteoporosis has advanced to Moderately severe and even my endocrinologist could care less about supplements or their value as he only wants to administer the cost prohibitive “bone mass stimulator” drugs of various varieties–all with serious side effects–but very lucrative for him and big pharma. There’s a serious problem in the medical education of doctors and health care delivery system for the general population of the US.

      • James A. Boatright

        Your light-skinned Northern European ancestors were able to thrive, however, because they consumed a lot of oily fish in their diet, by far the best natural food source of vitamin D.

  23. Betty

    To print the article (either to a PDF or to a Word doc) depress the left button on your mouse and highlight the article contents. Then depress the right button and choose either to Print (to PDF or paper) or Copy if you wish to create a Word doc.

  24. Manu. G. Mulchandani

    I read your article and became interested to keep it in my collection for my reading later & also tell my friends about this article. BUT BUT
    your arrangement is wrong because majority does not have printers and with limited funds we save these articles in our computers.

    Hence I could not keep your article in my computer & your knowledge spreading is does not allow me to transfer copy in my computer.

    Sorry with your arrangement I have no further interest.
    you are better organized for rich people.

    • Alexis

      You can print it to a file instead of to a printer, and thus have it on your computer. Alternatively, you could copy and paste the article into a blank word processing page, and then save it to your computer.

    • Cynthia

      If you print the articles to a Portable Document Format (PDF) file and save it on your computer, you do not need a printer with paper. You will just read it on your computer.

    • gzuckier

      Just save the page; your browser undoubtedly has a “save as” on the menu, save it as html, or mhtml, or even as a text file might be good enough in this case.