"In the depth of winter, I finally learned that within me there lay an invincible summer," said Albert Camus – who wasn't noted for his sunny disposition. And if Camus could find reasons to be cheerful, there's hope for us all. But it can be hard to stay healthy and upbeat as the days get shorter and the weather more vicious. So here is a distilled, evidence-based survival guide to winter – the things that work, and the myths that don't.
There's no doubt our vitamin D levels dip in winter, according to Simon Pearce, professor of endocrinology at Newcastle University. We need it for strong bones and a robust immune system, and deficiency has been linked to autoimmune conditions such as type 1 diabetes and multiple sclerosis. Most vitamin D comes from the sun and you can store some up by being outdoors in summer, though the trick is to get enough exposure to top up levels without increasing your risk of skin cancer. Russian prisons have apparently installed sunbeds for their sun-starved prisoners, which is misguided because the risks of sunbeds are thought to outweigh potential benefits.
Eating oily fish and fortified cereals or fat spreads can help boost levels; a portion of mackerel, sardines or wild salmon contains the recommended daily allowance of about 15 micrograms. But people older than 70 need 20mcg a day, and people who don't have any sun exposure won't be able to get enough from diet alone. If you shop around, you can get a month's supply of vitamin D supplements (10mcg a day) for less than £5. You don't get much wild salmon for that.
Exercise isn't quite the panacea it's claimed to be. There's no good evidence that it helps much if you're depressed. And you have to run quite a few miles (and not overeat afterwards) to shed weight. But a brisk walk, winter gardening or jogging outdoors has to be better than staying indoors from November to April. The sun is too low in the sky to help vitamin D, but it's surely good for morale. Regular exercise will also help to prevent joint and heart problems as well as obesity and diabetes. Anecdotally, many of us will vouch for the way exercise also helps to manage stress and anxiety and combat general grumpiness.
Garlic and chicken soup
Garlic doesn't protect against colds or help recovery once you catch one. It's antisocial enough to cough in someone's face when you have a cold, but unforgivable if your breath stinks. Chicken soup doesn't smell as bad but reports of its magical powers are exaggerated. Indeed, there are some hugely extravagant claims made for many foods and supplements, few of which stand up to scientific scrutiny. It's really hard for a healthy, omniverous UK adult to be seriously deficient in any essential nutrients, though your GP can do a blood test to check for anaemia if you're concerned. A cheap multivitamin, multimineral supplement will make sure you get the recommended daily allowance (RDA) of vitamins and minerals needed to maintain a robust immune system. Some people swear by the plant remedy echinacea; evidence suggests it may help you to fight off a cold but won't stop you catching one in the first place.
Flu jabs are a no-brainer for those who would be at risk of dying if they catch flu. The risk of serious side-effects is very low (one or two cases per million). The UK government is extending the flu vaccination programme to cover all children aged 2-17, starting with two- and three-year-olds this year. The rationale is that it protects individuals and reduces the risk of epidemics because kids spread viruses very effectively.
But should healthy adults get the jab? Peter Doshi, researcher at John Hopkins University medical school, says there isn't enough evidence to answer that. "My recommendation is that people do their own homework on this. Of the evidence, all I can say is that the proven benefits are far less than people realise – and public health officials state." Prof Simon Pearce, on the other hand, is having a jab because he doesn't want to catch flu or spread it to his patients.
Disposable face masks
Why do people wear face masks in the street? Is it self-protection or altruism? A large systematic review found that if you want to prevent the spread of bugs, it is best to target young children as they are most likely to bring infections into households. Kids don't wash their hands unless forced to, harbour bugs for longer than adults, and are very social creatures. So getting them to wash their hands and throw away snotty tissues is likely to be more effective than mask-wearing, which can be reserved for use in epidemics and high risk situations. If you have flu and don't want to spread it, you should forget the mask and stay at home.
Nice (the National Institute for Clinical Excellence) says people with Sad are no different to people who are sad. Seasonal affective disorder is a form of depression that particularly affects people in winter. But the recommendations are to try talking therapy, and possibly antidepressant drugs, rather than splash out on a light box. On the other hand, light boxes may do some good in the short term, don't cause harm if used correctly and may be easier to get hold of than NHS therapy.
I have my own, non-evidence-based approach to winter: big jumper, warm socks, chocolate raisins and red wine. But I have to emerge to go to work and for basic bodily functions. Oh to be a marmot; they hibernate for eight months a year.