Could the reason why some people put weight on in the winter be down to vitamin D?

I was having a casual conversation with a lady a few weeks ago on a cold and dull day. She mentioned that she was training for the London marathon (and racking up some significant mileage by the sounds of things) and eating what seemed to me to be a genuinely healthy diet (not rammed full of starchy carbs, for instance). Yet, she was putting on weight. I suppose it’s always possible, though unlikely, to build significant quantities of muscle through running. But, by her own admission, this lady felt that the additional weight was coming in the form of fat: she felt she could pinch more fat than before.

This lady was looking for an explanation, and one of the things that occurred to me at the time is that this lady’s paradoxical weight gain might have not much to do with her exercise and eating regime, but perhaps some more external facture. It was the depth of winter, after all, and it’s not so unusual for individuals to find they put on weight during the colder months.

There are several potential reasons for this. Some suggest, for instance, that during the winter we tend to gravitate to heavier, more calorific food, and at the same time are generally less active than when the weather is more agreeable. Also, one could argue that there is less ‘pressure’ to not be carrying excess weight during the winter, as it’s less likely our body will be revealed to others in public, like on the beach.

These things may be true, but is it possible that the weather itself has some role to play in weight? This may sound far-fetched, but a couple of studies recently have found that lower levels of vitamin D (as found during the winter) are associated with higher levels of body fat. One of these studies has yet to be published but can be read about here. The other was published in January’s edition of the Journal of Clinical Endocrinology and Metabolism [1]. The first study used teenagers as its subject, while the other used females aged 16-22.

Obviously, it’s possible that these results will not be seen in older individuals. And both these studies were ‘epidemiological’ in nature, and can only really tell us that there’s an association between vitamin D levels and body fat. It might be that vitamin D has no direct effect on body fat levels. One way to test this would be to see what effect boosting vitamin D levels (e.g. through food, supplements or sunlight exposure) has on body fat in the context of a randomised controlled trial. To my knowledge, no such studies have been published.

However, I was interested to read about a recently-published article in the journal Medical Hypotheses that puts forward the theory that vitamin D deficiency may actually cause obesity [2]. The idea put forward concerns the concept that there are evolutionary advantages to accumulating fat in the winter.

For a start, fat is a fuel store for the body, and this may have been especially important in evolutionary terms in the winter, when food is likely to have been in shorter supply than during warmers times of the year. Also, subcutaneous fat affords the body some insulation, which enhances the chance of surviving the harsh weather conditions winter can bring. Putting on weight also reduces the surface area to volume ratio of the body, which helps the body in terms of maintaining internal temperature and reduces the risk of hypothermia.

The author of this article suggests that lower levels of vitamin D may provide a signal to the body that winter is coming or has come, and triggers a switch to a ‘winter metabolism’ which predisposes to, among other things, weight gain. The suggestion is that ensuring optimal vitamin D levels may help to combat obesity.

To test this theory properly intervention studies are required. However, advances in medical science generally start as a hypothesis, and the one that vitamin D deficiency triggers fatty accumulation in the body seems reasonable. It might explain how someone training for a marathon during the winter months could end up putting on weight, rather than losing it.


1. Richard Kremer, et al. Vitamin D Status and Its Relationship to Body Fat Final Height, and Peak Bone Mass in Young Women. J Clin Endocrinol Metab 2009;94:67″73

2. Foss YJ. Vitamin D deficiency is the cause of common obesity. Medical Hypotheses 2009; 72(3):314-321

18 Responses to Could the reason why some people put weight on in the winter be down to vitamin D?

  1. Charles 16 March 2009 at 10:41 pm #

    excessive cardio–which by any definition is what a marathon is, as well as the training for one–leads to increased cortisol production, which leads to increased body fat. There are plenty of studies demonstrating that.

    This is not to dismiss your Vitamin D theory, in fact I would agree that it makes sense. But cardio is not an effective fat-loss strategy, despite everyone’s belief that it is.

  2. Dr John Briffa 16 March 2009 at 11:12 pm #


    I agree regarding the effect of cardio exercise: the evidence doesn’t point to this being a generally effective way to lose weight.

    Can you point me in the direction of some studies on exercise/cortisol/body fat?

  3. Chris 17 March 2009 at 3:27 pm #

    It would make sense in evolutionary terms if the human body had evolved some mechanism to fine tune metabolism or physiology to account for seasonal variation both in terms of ambient temperature and in terms of available food supply.
    Seasonality would be as much a part of habitat as any other recognised feature and what is evolution if it is not adaptation to a particular habitat?
    Is it not already recognised and generally accepted that deficiency in vitamin D can adversely effect mood, as in SAD?
    If vitamin D and SAD are linked by a mechanism that is a disruption to hormonal balance then the same, similar or consequential hormonal disruption may trigger a change to metabolism as per the quoted hypothesis.
    Prima facie, are there two likely explanations?
    1, either, the body handles calories differently and stores more of them as fat, or,
    2, the body is tricked into ingesting more calories through hormonal changes.
    Ah, we should not neglect that it could be a combination of both!

    The first requires there to be some “switching” effect between alternate metabolic pathways. This happens anyway as regulated by the hormone insulin. Would it also require that one calorie is worth more than another?
    The second requires only that our brain is tricked into making us eat more calories. In evolutionary terms this would make sense and would have served us well over millenia when we were at the mercy of the seasons. Laying down fat reserves on a seasonal basis would help combat lower temperatures and provide a buffer against food deprivation.
    Seated next to my radiator I muse that seasonality does not feature so prominently in my own habitat.
    Just as you regarded your jogger friend as being atypical to the extent she set you thinking so do I. Methinks she was not entirely truthful in revealing her eating habits

  4. Sherri 18 March 2009 at 7:43 am #

    Charles said “Methinks she was not entirely truthful in revealing her eating habits”

    Ah, yes, the old stand by accusation when anyone reports something that doesn’t follow the old calories in, calories out theory. Of course there is nothing wrong with the theory, it is just people lie. Sheesh! Maybe, just maybe, our bodies are a little more complicated than that???

  5. Chris 18 March 2009 at 6:37 pm #

    Sherri, My comment beneath Dr Briffas post was broadly supportive and underscored the likelihood that human evolutionary development would reflect some physiological adaptation to the seasons. There are, after all, other functions of the human body that are linked to natural cyclical events. In addition I concur with opinion which suggests there may be reason to caution over extreme physical activity whilst firmly subscribing to the widely accepted view that moderate exercise is beneficial to health.
    The proposition that our metabolism and/or eating habits may be influenced by exposure to available sunlight is an interesting one and (IMHO) highly likely, therefore, I would be interested in any explanation which suggested a mechanism.
    You will note that the contentious points in my comment were put forward as questions? My intention was to solicit opinion which would contribute to the development of this thread. I have a genuine interest in helpful debate.
    As for things being complicated, I agree entirely.
    I happen to subscribe to a view that you suggest you might agree with that “not all calories are, in fact, equal”, and my main interest is to understand the how and why. The calories out/ calories in theory whilst being somewhat simplistic is at least in line with the laws of conservation of energy. I see no reason to challenge those.
    If this poor lady were to read these comments she would no doubt be very self-conscious. I did not suggest she was deliberately untruthful. Neither was it my intention to sound overconfident but rather to express opinion and scepticism along two lines of thought.
    I find your comment interesting and revealing and would be gracious if you returned and directed me to some understanding of the complications of which you speak.

  6. Dana 20 March 2009 at 11:42 am #

    Here’s the problem though, Chris. Calorie theory assumes that every single scrap of food we eat will be broken down and used for energy. We have really bought into this idea, and yet we acknowledge that food is used for other things in addition to being a fuel source. For instance, we use protein to build muscle. The two concepts cannot co-exist. Either we burn all our food as energy or we only burn some of it as energy and direct some of it into other purposes.

    And if we’re directing some of the food we eat into non-energy-related purposes, by definition we aren’t using those calories.

    That’s the problem with calorie theory. And as we don’t know at any given time how much of our food becomes energy and how much becomes muscles or nerves or hair or hormones, it becomes very difficult to encourage weight loss via calorie restriction. Additionally, not knowing your own specific nutritional needs means that restricting calories may prevent you getting enough nutrients for proper body building and maintenance.

    This is why chronic dieters get sick in the long run, and permanently screw up their metabolisms.

    To Dr. Briffa: You should read Lights Out: Sleep, Sugar, and Survival by T. S. Wiley and Brett Formby, PhD. Wiley became infamous later for a bioidentical hormone replacement protocol that I understand caused problems for some women who used it, but her book about the effects of sleep deprivation on weight gain, diabetes, and metabolic syndrome is an eye-opener. Your vitamin D idea might be related (I checked the book out from the library and don’t have it in front of me) but also, not getting enough sleep means less melatonin production which cascades into a whole bunch of other nasty stuff happening. Or so she thinks. I would love to see some solid research done to investigate her ideas.

  7. Dr John Briffa 20 March 2009 at 6:53 pm #


    I bought ‘Lights Out’ perhaps 5 years ago and never read it (it slipped off my radar). I thought recently that I should actually read it, couldn’t find it in my office, but couldn’t remember the title of the book or its authors either! So your recommendation is perfect – thank you.

  8. Chris 20 March 2009 at 10:21 pm #

    “And if we’re directing some of the food we eat into non-energy-related purposes, by definition we aren’t using those calories.”

    Yes, Dana, the body is a complex adaptive system that has evolved ways to meet its’ energy needs quite elegantly and efficiently.

    What distinguishes a young child from a 49 yo male carrying 20 kilos overweight? Energy. Potential energy. At 20 kilos overweight an adult male has enough potential energy stored as body fat to meet the bodies energy requirements for 72 days. And yes, it is accepted that the body could not actually live healthily for 72 days purely on it’s own fat reserves. Starvation to that extent would result in muscle wastage as potential ENERGY from muscle is consumed to fuel the relentless energy requirements of cellular function.

  9. Chris 20 March 2009 at 11:55 pm #

    Consider this; seek out a photo of yourself from five years ago. How much have you changed? I’m sure you are very recognisable BUT describe to me where one might find a single cell captured in that photo that is present in you today! Our whole bodies are in a continual process of depletion and renewal. We take our continuity fro granted and overlook what is actually happening.
    The primary metabolic pathway that fuels our cells is elegant. The second pathway that converts energy from glucose to, what, about 250g of glycogen to be stored in the liver and muscles is equally elegant. This pathway frees up our time from continually have to ingest food to meet our energy requirements. It permits us to be active to do other things and it permits us to rest and sleep for the 7/8 hours that seems to be important for our well-being. Why cannot a newborn go long between feeds?
    Have you considered how our evolutionary lineage branched away from our primate relations 4-6mya? Have you wondered how a small advantage became a big one so that our species dominates the world today? Ok. Our brain swelled and our intelligence became more sophisticated. But how? Might you think that the brain size and liver grew in tandem? Does anybody know? What is more why should the answer be important to us today?
    The second metabolic pathway gives us a short term buffer for our hour by hour energy requirements.
    The third alternate pathway exists to cope with the case when we are well fed, when there is sufficient glucose to fuel our cells and when our glycogen reserves are full. In this case potentially toxic excess glucose is taken from the blood to be converted to body fat. At 8000+ calories per kilo body fat is a longer term buffer of energy that can be called upon later. Moderate body fat is essential now and conferred an evolutionary advantage as insurance against food scarcity.
    All this is regulated by hormones. It is magical, is it not?
    And I do not pretend to understand the regulative process. I wonder do alternate pathways occur with equal energy efficiency?
    I do not suppose that they do BUT inefficiency in conversion would result in energy ‘loss’ as heat. As we know temperature is critical to life and in humans must be kept fairly constant, therefore some compensatory process or management involving energy must be at work to regulate temperature.

    “This is why chronic dieters get sick in the long run, and permanently screw up their metabolisms.”

    I agree entirely, severe calorific excess or severe calorific restriction are not healthy. Why? They upset healthy hormonal balance and disrupt the ability of the body to continue to provide full service on metabolic regulation.

    The body is a complex adaptive system which, as was pointed out in the first line, is largely in equilibrium. Except it is not entirely. Once in adulthood we are all in decline to the degree that death is inevitable. Once we have reproduced we have no more influence upon evolutionary development of the species.
    Supplying our bodies with energy in balance with our needs is essential to permitting the body to function and settle to its’ most natural balance. Additionally those calories that supply a balanced energy need must contain sufficient (micro)nutrient density and diversity. So we are in agreement. And it all obeys the laws of conservation of energy; including the bit that the remnants of our existence and potential energy is either cremated or deposited in the ground.
    The challenge facing humanity in the 21st century is to understand why so many people struggle to exist at stable and healthy body weight.
    Your reference sounds interesting. I intend to seek that out.
    This event on April 4th looks interesting too.

  10. JD 21 March 2009 at 2:52 am #

    Regarding a calorie is a calorie. There are some who think that one who eats only fat and protein in excess can make one fat via the ASP pathway. When I posed this to Dr. Barry Groves he said what they have missed is the studies in the 60’s that extraneous fat can be excreted. He also said there is a lot we don’t know about human metabolism.

    Regarding aerobic exercise not leading to weight loss, there is a show on public TV in the US called NOVA where the staff trained for a marathon over like 10 months. Not one person showed a change in their body composition except for one woman who consciously tried to lost weight.

  11. Mike Abbotts 21 March 2009 at 7:24 am #

    Speaking as a fat but experienced marathon runner (“fat” as defined by professionally measured body fat percentage) I can say that I lost weight and fat in the 3 months leading up to each of my 40 odd road marathons. May I offer a simple explanation for the apparent contradiction of the combination of “significant mileage” and “a genuinely healthy diet” leading to weight gain. In my experience, most inexperienced marathon runners simply overestimate the calories they burn off during training – and consume too many calories in the aftermath. There is the feeling that provided the choice is “healthy” you cannot eat too much and, at the extreme, that you actually need to overeat to recover and build up your strength for the next training session. This phenomenon has got worse in recent years because of the plethora of high calorie “recovery” sports drinks and bars – a typical hypertonic drink will have around 240-320 calories per 500 ml ! (This is not an anti-sport drink rant – used correctly sport drinks are an essential part of distance running.)

  12. Dallee 21 March 2009 at 9:24 am #

    Thank you for writing about this subject. I have been following the low-carb Bernstein diet for diabetics ( and lost 50 pounds, which I kept off for an extended period. However, starting last November, my weight started creeping upward despite sticking to a diet of about 30 carbs per day.

    I’ve resumed Vitamin D supplementation and will see how that goes. However, I do have a question about the time to take a Vitamin D supplement.

    There are some indications that the supplement might be better taken in the evening — see European Journal of Pharmacology, Volume 460, Issues 2-3, 24 January 2003, Pages 171-175, ” Dosing time-dependent variation in the hypocalcemic effect of calcitonin in rat” (link: I know rat studies are not the most persuasive, but couldn’t find anything better for humans on my search.

    Do you have any thoughts on this issue? I would so appreciate any observations on this subject.

  13. Liz Smith 22 March 2009 at 5:12 am #

    When USA web sites mention Vit D they always say to get your levels checked. I can just see my doctor, if I can get an appointment with her, agreeing to me having a test. It will probably be dismissed as a new fad. Can tests be arranged privately through a research centre? I have done some muscle testing and with a pendulum and it says I can take some Vit D. I never use sun screen or spend hours cooking in the sun but it should not be taken like sweets and it would be nice to know what my level currently is. Any ideas folks?

  14. Natalija 23 March 2009 at 12:36 pm #


    I read this article and comments with interest.
    Personally I am overweight.
    However I want to point out the chain of events that lead to increased weight.

    I maintained the same weight for about 16 years and was heavily involved in extreme sports and marshall arts.
    One morning I woke up with a nasty pain in my back. My GP at the time claimed that it was due to the new mattress and I must pulled something.
    Days of rest were given and the back slowly appeared to be recoverd.

    I went back to excersizing. The more I excersized the more pain I had. Something else was happenning too, I was gaining weight and rapidly . You could almost see it in the mirror on daily basis.
    I started to reduce food intake rapidly while keeping the same level of excersizing, but was gaining weight and hurting a lot.

    I stopped excersizing as I become too heavy and in too much pain.
    Various blood tests and similar did not give any clue to why this happened and I was told that I am simply not telling the truth.

    The nutritionist I consulted after getting enough of doctors took some saliva samples and sent them to USA for anlysis.

    Cortisol levels were all over the place…
    I now control my weight by keeping to high suplementation and primal diet, but I never managed to get down to my “normal” weight and previous level of fitness.

    The story of John’s friend, rings too familiar. That is not to say that she will become overweight.

  15. Trinkwasser 27 March 2009 at 12:00 am #

    Seen this?

    it seems some UK people have successfully sent off for the test kit and returned their samples

  16. emma de morgan 7 May 2009 at 5:49 am #

    i had the idea myself that a lack of sunlight/vitamin d may cause our appetite to increase,because our bodies are desperate to replenish its stores. maybe a vit d rich diet in winter could helpprevent weight gain? i will certainly try it this coming winter as i ALWAYS gain weight in winter,from october to april…then suddenly it starts to drop off again!!

  17. Katharine 21 May 2009 at 2:39 am #

    NHS GPs can test your blood for vitamin d. It is a plain/neutral tube. I have tested a lot of patients and 9/10 have severe vitamin d deficiency. I live in Scotland where we have had no sunny summers for three years.

    I’ve been taking vitamin d supplements for over six months. So far I have not had any colds and my weight has been steady but alas has not decreased.


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