How the seasons affect diabetes

Managing glucose levels is one of the big priorities in the life of a person with diabetes. However, there are other factors besides diet and medication that can upset the balance. These include the often underestimated factors of the weather and the season of the year. Both the winter chills and the summer heat can influence glucose levels, and understanding seasonal changes can make a big difference in your health and wellbeing.

Why does glucose levels change according to the seasons?

Several clinical studies have confirmed that glucose levels and HbA1c tend to be higher in winter and lower in summer¹. This is due to a combination of physiological, environmental and behavioural factors.

• Temperature and insulin sensitivity: During cold months, the body tends to conserve energy and restrict the blood flow to the skin and limbs in a process called vasoconstriction. This phenomenon can interfere with insulin absorption, especially in people who administer it subcutaneously¹. Exposure to the cold can also raise the levels of cortisol, which is a hormone that increases glucose levels.
• Physical activity and lifestyle: Winter is also associated with less physical activity. Poor weather conditions and shorter days reduce the opportunities to exercise, which directly impacts glucose metabolism². By way of contrast, the good weather in summer usually makes people want to do open-air activities, walk, swim and generally move around, which improves insulin sensitivity.
• Dietary changes: People tend to eat more calorific and carbohydrate-rich foods in winter, such as soups with flour, chocolate and heavy meals in general. However, lighter, fresher diets are more common in summer, with larger amounts of fruit, vegetables and liquids being consumed³. This difference in dietary patterns has a direct impact on glucose levels.
• Circadian and hormonal rhythms: Exposure to sunlight regulates our circadian rhythms, which in turn affect hormones such as melatonin and cortisol. Reduced daylight in winter can affect these rhythms, which can contribute to lower insulin sensitivity and changes in glucose metabolism⁴.

What do the studies say?

Research published in Diabetic Medicine showed that average levels of HbA1c were consistently higher in winter and lower in summer, regardless of the type of diabetes¹. This seasonal pattern was observed in both children and adults.

Another study carried out by the PNAS magazine showed that circadian imbalances like the ones that arise during shift work or daylight saving times in winter can significantly reduce glucose tolerance and insulin sensitivity⁴. This phenomenon is more evident in winter, when people spend more time indoors and receive less natural light.

Moreover, a data analysis published in the International Journal of Environmental Research and Public Health found a correlation between extreme climates and glucose imbalance, suggesting that both extreme heat and cold can trigger imbalances in people with diabetes⁵.

Differences depending on the type of diabetes

• Type 1 diabetes: People with type 1 diabetes as they depend on exogenous insulin, are especially sensitive to seasonal changes, as they depend on external insulin. They need to be very attentive to the need to change doses according to the season.
• Type 2 diabetes: Winter can exacerbate insulin resistance, a hallmark of type 2 diabetes. Keeping active in colder months is essential for glucose management.
• Gestational diabetes: Although this type of diabetes is temporary, it can also be affected by seasonal changes, especially if the pregnancy takes place in summer or winter. Extreme temperatures may worsen glycemic variability.

Recommendation for better seasonal glucose management

In winter:

• Monitor your levels more often, especially if you notice an increase.
• Increase your physical activity indoors: walk around at home, do online exercise routines or use an exercise bike.
• Adapt your diet: include soups with greens, legumes and avoid consuming too many refined carbohydrates.
• Check your insulin doses with your endocrinologist, as they may need adjusting.

In summer:

• Stay well hydrated, remember that dehydration can increase glucose levels.
• Make the most of fresh seasonal fruit, but don't overdo it with fruit with a high glycemic index, such as mangos and watermelon.
• Do exercise at safe times of the day (early morning or late evening) to avoid heatstroke.
• Check your medications if you are going to be exposed to direct sunlight or high temperatures, as some medication (applies to certain oral antidiabetic drugs or insulin) may deteriorate with heat.

Glucose management is not static: it changes with the seasons, the weather and our daily habits. Finding out how the environment can affect your body enables you to plan ahead and make effective decisions. People living with diabetes and health professionals should take these factors into consideration to achieve a more personalised, effective seasonal management of their condition.