More evidence links higher vitamin D with lower risk of infection

Infections such as cold, flu and chest infections are generally more common in the winter. One traditional explanation for this is that when the weather is cold, people spend more time indoors. The more time people spend with each other in close confinement, the more likely they are to catch something, as well as pass an infection to someone else.

This explanation almost certainly has merit, but it’s unlikely to be the whole story either. In recent years some scientists have suggested that the upsurge in infections seen in the winter may be due to lower levels of vitamin D. Vitamin D, among other things, facilitates the production of ‘anti-microbial peptides’. As their name suggests, these natural substances work like natural antibiotics to counter infecting organisms.

Prior to the advent of antibiotics, sufferers of tuberculosis might be sent to a sanatorium for rest, recuperation, and a healthy dose of sunshine. It is possible the when individuals recovered from their infection in this setting, at least some of this had to do with the higher levels of vitamin D they would have attained by taking in more sun.

I was interested to read about a recent study in which the relationship between vitamin D levels and ‘respiratory infections’ in 6,789 British adults [1]. The researchers, from University College London, found that vitamin D levels and infection risk had a linear relationship, which in this case meant that the higher levels of vitamin D were, the lower the risk of infection.

For each 10.0 nmol/l (4.0 ng/ml) increase in vitamin D (25-hydroxyvitamin D), risk of infection was 7 per cent lower. There was a similar relationship with lung function too, with higher vitamin D levels being associated with better lung function.

I have previously reported on another study which found higher levels of vitamin D were associated with reduced risk of flu and reduced duration of the illness should they get it.

These studies are epidemiological in nature, and therefore cannot be use to conclude that vitamin D prevents infections. However, there is at least a plausible mechanism through which vitamin D might do this. We also have this study which found that vitamin D supplementation had some ability to reduce risk of flu in children.

In February 2009 I had my own vitamin D levels checked and found these to be crashingly low (15 ng/ml). I have been supplementing with vitamin D ever since (most of the time, I take 5,000 IU a day). In the whole of the my time taking vitamin D (getting on for 2½ years) I have experienced one infection – a viral cold/flu illness that lasted 4/5 days in total. Previously, if my memory serves me correctly, I would get about 2 infections a year. Nothing scientific about this, of course, but at least consistent with the idea that maintaining optimum vitamin D levels could help to keep us free from infection.


1. Berry DJ, et al. Vitamin D status has a linear association with seasonal infections and lung function in British adults. British Journal of Nutrition 6 June 2011 [epub]

30 Responses to More evidence links higher vitamin D with lower risk of infection

  1. Paul Stevens 7 June 2011 at 9:39 pm #

    Evaluation, Treatment, and Prevention of Vitamin D Deficiency: an Endocrine Society Clinical Practice Guideline

  2. Reijo Laatikainen 8 June 2011 at 4:34 am #

    Very interesting again. Thanks! I guess you are already familiar with this RCT -based meta-analysis. -Reijo

  3. Reijo Laatikainen 8 June 2011 at 4:38 am #

    I’m sorry, I omitted the link to the meta-analysis on vitamin D and respiratory infections:

  4. Feona 8 June 2011 at 7:52 am #

    I’m now taking more Vit D than previously and had noticed that my susceptibility to colds etc seemed to be less. I’d put it down to not travelling on public transport as often as I used to, but maybe the extra D is having an effect too. Thanks for posting such useful and informative items.

  5. DoctorM 9 June 2011 at 10:07 pm #

    I am sure that vitamin D contributes to some extent to the avoidance of colds and other diseases and conditions – but this is only part of a much bigger picture of maintaining immunity. A diet high in nutrients (vitamins, minerals, phytochemicals etc) from a broad range of all types of raw or lightly cooked natural fresh and some dried plant, animal and other (fungi, seaweed etc) wholefoods is what provides immunity. The modern western diet consisting almost entirely of nutrient poor refined and processed ‘foods’ loaded with sugar, refined flour and refined fats and oils and chemical additives, is so low in nutrients and so far from nature that it is no wonder we get sick. Regular exercise, spending time outdoors (for vitamin D) and taking dietary supplements will also help maintaining immunity but this is not nearly as important as moving away from the standard nutrition poor western diet to a nutritious wholefood diet.

  6. gill oliver 10 June 2011 at 10:26 am #

    Dr Briffa could you please explain what 5000 iu means please, I am taking two tabs per day of combined vit D and C. which the carton says is 800.0mg vit c and 5.0 iu vit d, is this enough.

  7. John Briffa 10 June 2011 at 10:29 am #


    IU stands for ‘international units’. The dose someone needs depends on many factors – especially their baseline levels. However, if your levels are low (only a test can tell you), 5 IU is not going to be enough (it’s 0.1 per cent of the dose I take).

  8. Hannah Hutton 10 June 2011 at 11:12 am #

    I’ve also noticed this difference with my 14yo son who used to become really ill with flu/respiratory illnesses in the winter (he also has asthma), but these have virtually gone since I started giving him Vitamin D3 supplements. It’s difficult to know how much to give children, especially as I don’t want them to have regular blood tests to check their levels (not that these kinds of checks are on offer anyway!). The ones I buy are 2400iu and I only supplement over the winter, from about November onwards and probably about every other day. It would be great if there was more advice available, on dosage, amounts for children, what to do if you’re not having regular blood tests, D3 over D2, etc.

  9. tal 10 June 2011 at 11:20 am #

    My family members have been following the protocol recommended by Dr John Cannell for the last 2 winters with great results: not a cold or infection of any sort although people around us succumb.

    Cannell recommends 60,000 IU in divided doses over 3 days at the first sign of of infection. I usually throw in several grams of vitamin C to augment the D but the most interesting aspect for me is that you can ‘feel’ the effects of the vitamin D wearing off as the time for the next dose approaches. At the end of 3 days, wellness.

  10. Penny Vinden 10 June 2011 at 11:37 am #

    Have you seen this article about low absorption rates of Vit D in spite of sun exposure? More reason to get tested!

  11. Jennifer Eloff 10 June 2011 at 12:43 pm #

    I believe it. We’ve been taking vitamin D3 – is that better than plain Vitamin D or not? My DH seems to think so.

  12. Will 10 June 2011 at 1:36 pm #

    An interesting study, but sadly not supported by this supplementation trial:

    A randomized controlled trial of vitamin D3 supplementation for the prevention of symptomatic upper respiratory tract infections
    M. LI-NGa1, J. F. ALOIAa1 c1, S. POLLACKa1, B. A. CUNHAa2, M. MIKHAILa1, J. YEHa1 and N. BERBARIa3

  13. Sue 10 June 2011 at 3:33 pm #

    I’ve just been listening to your podcast, which mentions that GPs may do a 25 Hydroxy Vitamin D test now that more information is readily available to them.

    Unfortunately, when I asked my GP for the test last Autumn because I had been taking high dose Vitamin D3 for a while, she said that the GPs in Bedfordshire have been told by the hospital lab not to allow their patients to have the 25 Hydroxy-vitamin D test unless their Calcium levels are low. I suspect quite a few enlightened patients have been asking for the test which prompted this policy.

    The silly thing is that you can have a normal calcium level yet have a severe deficiency in Vitamin D.

    Three of my clients, who are quite knowledgeable about healthy living, had the 25 Hydroxy Vitamin D test at a private lab, last October, and all three were very deficient. Thankfully, when I had the test, my result was excellent.

    If GPs were allowed to order the test for their patients and corrected any deficiencies, surely they would have far more healthy patients who would need fewer (if any) drugs!

  14. David 10 June 2011 at 3:34 pm #

    I took 10,000 iu for 3 consequetive winters and didnt get ill once for 3 years, not even a cold, whereas before that I would get at least 2 colds a year. I dropped the dosage to 2000iu and got a cold that winter so am now back up to 10,000 iu a day in Winter.(And plenty of sun in the summer)

  15. frances 10 June 2011 at 3:53 pm #

    I’ve also been taking 5000iu a day for nearly 2 years…and had no colds etc in that time. However, lately have been suffering with aching joints and on reading further on the Weston Price site and others, it seems that Vit A particulaly in the form of cod liver oil also needs to be taken with the Vit D for it to be effective. Do you know any more about this as there is a lot of reading to get through and understand?!

  16. mrweetabix 10 June 2011 at 5:31 pm #

    Recent vitamin frenzies over the recommendations for the widespread use of antioxidants, folic acid, vitamin E, and beta-carotene provide lessons about vitamin supplements that must not be forgotten. When the proper research was finally done, the results backfired. More heart disease, cancer, and overall death were discovered in those taking these isolated concentrated nutrients (4-9). Each of the above nutrients is originally found in edible plants. In these perfect packages these nutrients provide for excellent health, prevent and cure diseases, and prolong life.

    When consumed as isolated concentrated nutrients wrapped in a pill-casing, vitamin D supplements cause nutritional imbalances, which leads to metabolic sicknesses. At dosages considered safe, an increase in “bad” LDL-cholesterol, prostate cancer, immune system suppression, autoimmune diseases, gastrointestinal symptoms, kidney disease, and calcium stones has been observed (10-16). The adverse effects of vitamin D therapy are understudied, underestimated, and underreported

  17. ethyl d 10 June 2011 at 6:16 pm #

    Whenever I feel a cold coming on I begin taking larger than normal doses of D3 (normal dose is 4000IU daily), say, 16,000 daily for a couple of days, and my cold symptoms usually go away. If a cold does occur anyway, it’s nowhere near as severe or long-lasting as the ones I used to get. I haven’t had a sinus infection or bronchitis since supplementing with D3, ilnesses which used to be a given every winter, sometimes two or three times in a season.

  18. Jennifer Eloff 10 June 2011 at 10:50 pm #

    Interesting, Ethyl. Thanks for sharing.

  19. Frederica Huxley 10 June 2011 at 11:39 pm #

    @frances- I have read that the vit A works against the vitamin D in cod liver oil – please read Dr Mercola on this subject:

  20. DoctorM 11 June 2011 at 8:07 am #

    Quite frankly, if one gets colds one is short of a whole spectrum of nutrients including but not limited to Vitamin C, bioflavonoids, zinc, Vitamin A, Vitamin D and many others. Get the diet, lifestyle and supplements right as per my previous commnent. No point in obsessing just with Vitamin D.

  21. John Briffa 11 June 2011 at 2:16 pm #


    If you’re going to just cut and paste from the internet, at least attribute it to the author. Otherwise, it’s called plagiarism.

  22. Liv 11 June 2011 at 10:05 pm #

    Um I get loads of Vit D as I live in Africa and live an outdoor lifestyle (as we all do here) and really we get masses of viral (it seems) flus and colds as a community, the same as I’ve experienced in UK (where I’m from). In fact I very nearly died from a viral infection resulting in ARDS last Nov- the dry and hot season. Vitamin D is important, I believe, but I/we have sunshine all-year round so I fail to believe Vit D in isolation provides sufficient protection. I have a 5 year old daughter who also gets the same round of bugs as everyone else and I’m fairly militant re nutrition etc. My point is it is easy when living in UK when your sunlight exposure is pretty poor to assume that it is the main causative issue- I’m not convinced. I’ve lived in sub-tropical Africa for 6 years and coughs, colds and sniffles still seem to affect my community in exactly the same way as in UK.

  23. Reijo Laatikainen 13 June 2011 at 6:30 am #

    Doctor M has got a point, there’s so much more than just vitamin D. See my slides on the topic if intrested

  24. John Newsome 13 June 2011 at 10:06 am #

    Dr Briffa,

    Recommended dosage levels on shop bought supplements are much lower than 5,000 IU per day. How accurate do you believe these levels to be? Presumably, you regard them as wrong as you take a much higher dose.

  25. John Briffa 13 June 2011 at 10:21 am #


    I’m not sure what you’re asking. Is this a question about what I believe optimal intakes to be, or whether the stated amounts on supplements is to be trusted?

  26. John Newsome 13 June 2011 at 12:08 pm #

    Dr Briffa,

    I would be interested in your opinions on what optimal intake is and how seriously we should take the information on supplements. I get psoriasis and the anecdotal evidence (so far) leads me to believe that Vitamin D helps it. As such, I am interested in whether you would suggest taking Vitamin D permanently or just when it flares up?

    I am taking 3,000 IU’s at the moment but most supplements state a recommended dose far lower than that. Could I also ask what product you use to get your daily 5,000 IU’s?

    Many thanks

  27. Andy 23 June 2011 at 10:35 pm #

    Did they get infections because they had lower Vitamin D levels? Or did the infection cause the them to have a low vitamin D level?

  28. Rebecca 11 September 2011 at 7:58 pm #

    John, I get 5000iu from – they have Vitamin D imported from USA. You’re right, its hard to get that level here in the UK


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