‘Tis the Season to Be… Healthy?

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Now that December has rolled around, those of us living away from the equator may be looking forward to sunshine and swims, or cosy nights and warm drink delights. Along with the respective pleasures summer and winter bring, there are some unique health considerations to each season. Here we look at a few common issues that, if you keep on top of, will help you see through the end of this (weird) year healthy and happy.  We also explore our as yet limited knowledge regarding seasonal changes (or lack thereof) to our microbiome- an area with potentially significant implications.

Key Points:

  1. Summer increases the risk of getting sunburn and developing skin cancer, and of experiencing heat stress and food poisoning. Sun protection, keeping cool, hydration, and keeping your food in safe temperatures is critical.
  2. In winter there are increased risks of cardiovascular disease and stroke, as well as infections, vitamin D deficiencies, and seasonal affective disorder. Maintaining a healthy lifestyle and seeking the guidance of a health professional are crucial first steps to minimising these risks.
  3. The seasons could impact our health through our microbiome. More evidence is required for how the microbiome changes throughout the year in urbanised populations, and what dietary and other factors can be used to capitalise on potential benefits.

Summer Health

Sun, swims, smiles and…


Yes, we all know that the UVA and UVB radiation we enjoy from the sun contributes to sunburn, and, more seriously, DNA damage possibly leading to cancer. And yet, melanoma, basal cell carcinoma and squamous cell carcinoma have been becoming more common. So it appears that somewhere, somehow, there’s a gap through which the slip, slop, slap, seek, slide message is slipping through. 

A dissection of the reasons for this trend and what public health initiatives may correct it is beyond the scope of this post. However, focusing on the practical steps you can take:

  • Apply sunscreen daily when the UV index is 3 or more. Get into the habit of doing so before you leave the house in the morning. You can find the UV index on many weather webpages, or on specialised apps.
  • Choose a sunscreen that is of SPF30 or above… Be aware that SPF50 only offers marginally greater protection. i.e. SPF50+ filters out 98% of UVB radiation, compared to SPF30 which blocks out 96.7%. 
  • It may be that you need to use more sunscreen than you think… Research has indicated that people on average apply 0.8mg of sunscreen per square centimetre of skin, whereas the recommendation is for 2mg. Before you attempt to calculate just how much skin you have and order some highly precise scales, try Australia’s Cancer Council rule-of-thumb: apply approximately a teaspoon to each of your limbs, back, front and face. 
  • Reapply your sunscreen every 2 hours. It can be easy to forget to do so while you’re out and about, so perhaps setting a reminder on your phone may help. 
  • Wear clothing, hats, and sunglasses (it’s worth investing in a pair with a UV protection index of 400+), and seek shade wherever possible. 

Heat stress

This one is hardly surprising, but with hot temperatures and days spent lapping up the sun there is a risk of heat stress. This may be mild- you may experience heat cramps or heat exhaustion, marked by headache, weakness, dizziness, edema, tiredness and an inability to continue activity. 

Or you may experience a more serious problem- classic heat stroke. Here your body is simply incapable of ridding itself of all the heat stress you’ve taken on from the environment. Your core body temperature increases. When it reaches 40 degrees there is a toxic effect on cells… an inflammatory response is prompted… and- if unchecked- you may experience failure of multiple organs and even death. For example, blood and therefore oxygen supply to the intestines is reduced (blood flow is diverted to the skin in a desperate attempt to get rid of heat). This injures intestinal calls, they become more permeable and toxins may leak into the body’s blood supply. The brain is also very sensitive to the heat, so there may be confusion, delirium, behaviour changes, dizziness, weakness, agitation, combativeness, slurred speech, nausea and vomiting. Seizures and incontinence are even possible, although they are more common from excessive physical effort (exertional heat stroke) than classic heatstroke.

Who is most at risk of classic heat stroke?

The elderly, ill people, those unable to look after themselves and children. Children absorb heat at a faster rate, as they have a high skin surface area relative to their mass. In addition, their potential to lose heat is low: they sweat less than adults and they have a low blood volume relative to their body size, limiting their ability to lose heat by conductance through blood. 

It can also be a particular problem in inner cities and during the heatwaves which are becoming increasingly common thanks to climate change.

How to manage heat stress

The best way is to prevent it to begin with… use air con or fans,take frequent cool showers, exert yourself less on hot/humid days and avoid training at the peak of the day. You can also look out for the vulnerable by increasing social contact and checking in on elderly people regularly. 

If you do experience heat stress, hydration and moving to a cool area are essential, as soon as possible. Medical care must be sought for anything beyond mild symptoms.

Food poisoning

Seeing as heat fosters replication of microbes, it’s not surprising that food poisoning is more common during the summer months. Taking extra care of food handling and temperature is key. You may need to lower the temperature of your fridge, and for situations such as picnics put perishable food in a good old esky (or use ice packs). A more comprehensive outline of food safety measures can be found here

A British study from 2001 raised the possibility that it’s not just food safety in the home or at the point of consumption that may be the culprit- and that there is risk in the food production and distribution parts of the chain too.  Asides from making judicious choices, it may be worth reporting food poisoning cases that you believe can’t be accounted for by your own food handling practices to your relevant authority. If a pattern with a certain company is discovered, corrections can be made which may protect others. 

Summer SAD (Seasonal Affective Disorder)

Although it is less common than SAD during winter, people can experience poor appetite, weight loss, insomnia, agitation, restlessness, anxiety, and occasionally violent tendencies. If you or someone you know experiences this, consult your doctor or a helpline. (Incomplete) lists of international helplines have been compiled here and here

Winter health

Winter is often associated with higher morbidity and mortality- and not just due to seasonal infections. The weather itself can affect your physiology in diverse ways. 

Perhaps ironically, ill health is particularly seen in countries with milder climates. 

Increased disease burden

More cases of cardiovascular diseases and stroke are reported during the winter months. A complex network of factors are thought to contribute to this. For example, temperature, lower vitamin D levels, increased cholesterol levels, reduced physical activity, increased levels of blood coagulants, hormone fluctuations, variations in air pollution levels, and certain microbial infections can all lead to pathological physiological responses. 

Optimising the fundamentals of your lifestyle by staying physically active, eating well, managing stress, not smoking and limiting alcohol consumption can go some way towards reducing risk for such diseases. It’s also advisable to get a medical review with your doctor, to identify any potential hidden risk factors you may have, such as high blood pressure or cholesterol, and plan accordingly.

Altered immune function 

The immune system varies throughout the year. For example, in winter it is more pro-inflammatory, the microbial-killing activity of neutrophils (a type of white blood cell) decreases, and the production of immune-signalling molecules changes. The above-mentioned old lifestyle fundamentals are also valuable in supporting your immune system.

Vitamin D

Those of us who live further from the earth’s equator are more likely to see their vitamin D drop during winter, due to less sun exposure. Vitamin D levels can have implications for your bones and throughout your body. Thus, in winter, you want to get time out in the midday sun where possible, with arms or other areas exposed. The amount of time required will vary according to your colouring and latitude. According to Osteoporosis Australia, for example,  people with fair skin living closer to the equator may need as few as 7-30 minutes most days, while people with dark skin living at higher latitudes may require up to a few hours’ exposure. 

When this is impractical, increasing your vitamin D intake should be considered, through natural food sources (eg: fatty fish, cod liver oil, egg yolks, mushrooms, beef liver), fortified foods or supplements. 

The UV index can be used as a more objective indicator of how much sun the ‘average person’ (if such a thing exists) requires. On days when the UV index is less than 3, more time will be required.As mentioned above, weather sites often provide information on UV index; alternatively, there are a number of UV index apps available.

Winter blues- SAD

Seasonal Affective Disorder is most common during the short days of winter. People with SAD have more difficulty adjusting their circadian rhythm to the reduced day length and express symptoms of depression, fatigue, hopelessness and social withdrawal. It appears to occur more often in women and in those farthest from the equator.

Some studies suggest a reduced activity of the feel-good hormone serotonin may contribute to SAD, possibly as a result of reduced vitamin D levels.  An overproduction of melatonin, a hormone associated with drowsiness and lethargy, may also be a culprit. 

If you suffer, light therapy, vitamin D supplements, counselling, keeping physically active and medical treatments can help. 

Light therapy can be achieved using commercially available light boxes or light rooms (available in Scandanavian). These mimic the sun’s spectrum of light and should be used first thing in the morning to maximise effects. However, there are risks involved, so light therapy should be monitored by a health professional. For example, hypomania and suicidal ideation may occur particularly in the first days of light therapy. It should also be avoided if you are on medications that make you more sensitive to the light, such as lithium, melatonin, phenothiazine antipsychotics, and certain antibiotics.

If you or someone you know experiences this, consult your doctor or a helpline. (Incomplete) lists of international helplines have been compiled here and here

Changing seasons, changing microbiome?

The composition of your microbiome is influenced by a number of factors, including day length, vitamin D levels, diet, physical activity, nature of infections (winter respiratory vs summer gastrointestinal infections), and other things that tend to vary with the seasons. 

However, there is not yet enough research to predict how the microbiome of people from developed, urbanised societies will differ between winter and summer. This is because human studies thus far were limited to unique populations with substantially different environments and lifestyles. For example, the microbiome of the Hadza people (hunter-gatherers) of western Tanzania clearly varies with the season-  and from ours. Their diets also vary a lot between seasons, based on what is available in the wild.  Likewise, there have been seasonal differences in microbiota observed among agricultural Hutterites of the USA, an ethnoreligious group who live communally, a low-income and primarily agricultural population of Ukrainians, and subpopulations of  Japan and Mongolia.

In contrast, urbanised populations are somewhat removed from the influence of climatic factors. For example, the relatively stable supply of fruit and vegetables to people in developed countries mean our intakes tend not to change very much. This could be related to a loss of microbiome diversity. Interestingly, the Inuit from the Canadian Arctic- a traditional hunter-gatherer group- did not display changes in their microbiome between the seasons. One proposal is that this is because their diet is becoming increasingly westernised.

Thorough studies amongst urbanised populations should be done to determine if and how their microbiome changes throughout the seasons. The precise implications for our health should then be mapped out, and the relative contributions of diet, other lifestyle and environmental factors determined. Then we may be able to make concrete recommendations for you for different times of year. In the meantime, increasing the variety in your diet and eating more seasonal fruit and vegetables, and ensuring you get enough physical activity and vitamin D, would be sensible steps to take.

The Verdict

A healthy summer means enjoying the heat and sun, but also taking precautions to avoid exposing yourself (and your food) to too much. Maintaining a healthy lifestyle and healthy levels of vitamin D can help offset some of the immune-related and non-infectious health risks associated with winter. We should also be aware that SAD can occur during either summer or winter, and should we see signs, seek assistance in the form of medical care, counselling and/or light therapy as appropriate. Eating seasonal produce may help support the microbiome that supports us.

What health matters do you need to look out for this season?


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