Why might shift-workers be at increased risk of multiple sclerosis?

When I was a junior doctor, like a lot of junior doctors, I was not thrilled when my bleep would go off in the middle of the night to be called to attend to a sick person. It was not uncommon for this to happen after a full and busy day at work. Sometimes, little or no sleep may have been had the night before. And perhaps the night before that too. A weekend shift might entail starting work on Friday morning and not finishing work until Monday night. I distinctly remember senior colleagues telling me that these sort of work practices were character-building and never did them any harm. Well, that might be the case, but my belief is that sleep deprivation almost certainly harmed (and killed) patients.

Doctors hours have changed now in the UK, and along with nursing staff, tend to work shift patterns. That could mean working during the day for a few days with no night duty. But, alternatively, it could mean working at night, with the idea that sleep will be had during the day. Health professionals in hospital are, obviously, not the only people who might work this way. Security staff, policemen and women, pilots and cabin crew, and factory workers, for instance, may also spend periods living a nocturnal existence.

Getting the body clock to bend to our will is not always easy, with the result that those working night shifts, at least in the short term, can simply lack sleep. This is likely to have consequences to for energy and vitality, as well as general health. There has been some discussion in the scientific literature that shift-work is associated with an increased risk of chronic disease including breast cancer. Some have suggested that this might have something to do with disruption in the secretion of the ‘sleep hormone’ melatonin. Melatonin is an ‘antioxidant’, and in theory may help prevent cancer as well as other chronic diseases.

I was interested to read about a recent study in which shift work in adolescents was found to be associated with another chronic disease – multiple sclerosis [1]. Melatonin is mooted as perhaps having a role here in this paper, as is the tendency for disruption of sleep to lead to enhanced inflammation in the body.

I was wondering, though, whether another explanation for this association might be to do with sunlight exposure and/or vitamin D. Previous research has linked sunlight and vitamin D with reduced risk of multiple sclerosis. See here for more about this.

Other evidence in animals suggests that sunlight might exert a protective effect here in a way that has nothing to do with vitamin D. See here for more about this.

Multiple sclerosis tend to be most common in northerly latitudes (see map below).


global prevalence of multiple sclerosis


As it happens, the research linking shift work with multiple sclerosis was conducted in Sweden, which may be relevant. Sunlight is a relatively precious commodity there, and someone working at night and sleeping during the day will be at risk of lacking in sunlight exposure and vitamin D, I’d say.

This is all speculation, of course, but it occurs to me that those engaged in shift work might make a conscious effort to get safe exposure to sunlight when they can. And it might be an idea to have their vitamin D levels checked, and think about supplementing with this nutrient if low in an effort to maintain more optimal levels.


1. Hedström AK, et al. Shift work at young age is associated with increased risk for multiple sclerosis. Ann Neurol. 2011 Oct 17 [Epub ahead of print]

2 Responses to Why might shift-workers be at increased risk of multiple sclerosis?

  1. DoctorM 21 October 2011 at 12:49 am #

    Man and its predecessors evolved not only on a natural diet but also in a natural enviroment and with a natural level of activity. We hear huge amounts about paleo diet but almost nothing about paleo environment. We argue about whether foods which are less than 10000 years old are healthy for humans but there is scarcely any argument about whether living indoors in the artifical light, with shift work, irregular hours , lack of sleep, inactivity, sitting in cars rather than walking, watching telvision, sitting at computer screens, jumping time zones, stress, lack of companionship, etc etc is healthy even though these deviations from nature have occurred – in the most part – over a couple of hundred years !
    To a naturopath and student of human evolution it is so obvious that these deviations from our natural condition are a big risk factor for human health – perhaps as risky as modern industrial food. What is wrong with waking with the morning light, being outdoors and active in the day (with ones companions) and going to sleep at dusk ? – Why would one choose to do anything else ? (OK OK I know the answer is that this is unavoidable due to the constraints of modern industrialised life).

    Science aims to compensate for failings of modern life by identifying isolated substances (medicines, supplements) with which to treat ailments of modern life. Vitamin D has become fashionable of late but vitamin D is only one line in a huge spectrum of micronutrients (to use a reductionist term in want of a better term) that we need. Actually I do not think that we should think of food (ie natural wholefoods) as a combination of nutrients but as a low entropy (ie highly ordered) material which is precisely matched to our nutritional needs ie a carrot or a fillet of mackerel is a carrot or a fillet of mackerel and of very low entropy – it is not to be thought of as (an implicitly high entropy) combination of just carbs, protein, fat, vitamins and other micronutrients. The presence or absence of individual vitamins etc should be seen as an indication of the differences between different types of food – so the presence of vitamin D in mackerel is an indication that it might be a healthy nutritious food even though it is not the vitamin D of itself that makes it healthy.

    So I think it is very unlikely that vitamin D alone as a supplement will have a big impact (though mackerel might) – and certainly not be the only answer to lack of sunlight. But I absolutely agree with Doctor Johns conclusion in his final paragraph – and in spite of the uncertainties that taking the right type of vitamin D (D3 ?) as a supplement probably reduces risk for many people. There is also a risk that excess vitamin D supplementation may be harmful – we tread a narrow line.

    However I feel so uncomfortable that we evolved so far from paleo enviroment as well as paleo food that we have to seek ‘line spectrum’ patches for our ailments in a, by and large futile, attempt to compensate for extreme dietary and environmental failings. No one substance, or combination of isolated substances is likely to be a panacea (I think the polypill is a disaster waiting to happen and hope it doesn’t happen) – though many will of course receive respite from their current ailments, others may not and many will receive unwanted side effects.

    If we believe in paleo diet I think we we should also believe that paleo enviromnent is just as important an objective to strive for. Fix the problem – don’t just treat individual ailments

  2. audrey wickham 21 October 2011 at 12:13 pm #

    An Australian endocrinologist who was working at St. Thomas’ when I was a patient there told me he was so tired when he was a junior doctor working on wards in Oz that he prescribed two diabetic patients with insulin then almost gave them the others’different amounts. He was saved from his mistake because an Australian nurse(they are more inclined to think for themselves than European nurses)pointed out to him his mistake.

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