For better or worse? How summer impacts your physical health

For the summer of 2020, the most pressing health concern probably won’t be sunburn or bug bites but whether the new season will bring a reprieve from the spread of COVID-19. Unfortunately, summer heat may not be the answer to quelling the coronavirus, according to research published in the Canadian Medical Association Journal.

In the study, researchers examined a cohort of 144 geopolitical areas worldwide comparing cumulative counts of the disease with humidity, latitude, temperature, restrictions of mass gatherings, school closings, and measures of social distancing. They found that epidemic growth of COVID-19 was not linked to latitude and temperature. However, public health interventions did reduce spread.

So, summer will likely not put a dent in the spread of COVID-19, as some hoped. But what about the other health effects of summer? Is summer better for your health, or worse? It’s both. Summer is a better season for some health conditions but worse for others.

Cardiovascular function

Is summer harsher on your heart than other seasons? In a study published in Hypertension Research, Taiwanese researchers examined the association between seasonal variations in cardiovascular biomarkers among 72 participants working in a forest environment.

They found that during winter, blood pressure readings were elevated, as well as systemic vascular resistance and brachial-ankle pulse wave velocity. Furthermore, heart rate, left ventricular contractility, and cardiac output were lower in winter than in summer. The researchers also found that lipid levels, white/red blood cell counts, and platelet counts were all higher in winter. Overall, they concluded that winter was a time of higher vascular stress and increased risk of atherothrombosis.

The authors served up certain hypotheses to explain their findings. For instance, cooler winter temperatures are linked to increased weight circumference because people need to eat more to maintain warmth. Furthermore, winter leads to decreases in heart rate, cardiac output, and left ventricular contractility to avoid the need for energy consumption in cold weather.  Winter also induces vasoconstriction to keep central organs perfused, which in turn leads to increased blood pressure.

Lung function

Every physician knows that cold air triggers bronchoconstriction, which is of particular concern in those with asthma. But, warm ambient temperature also impacts lung function.

In a high-powered study published in the European Respiratory Journal, researchers mined the Framingham Heart Study for data on lung function and compared it with satellite temperature data. 

According to the researchers, “In this cohort of generally healthy adults residing in the Northeastern US, warmer temperature was associated with lower lung function, after controlling for season and other confounders. This negative relationship between temperature and lung function was steepest in the cooler temperature range (<10°C), and present during winter and spring, but not summer. People with asthma and COPD had similar associations between temperature and lung function as those without these obstructive lung diseases,” they wrote.

They noted that their finding aligned with a number of studies that have found linear associations between higher daily outdoor temperatures and worse respiratory outcomes, including lung function, respiratory symptoms, and respiratory hospitalization.

Though the researchers didn’t track time indoors vs outdoors, they hypothesized that increased time spent outside or in front of open windows led to greater allergen, pollutant, and pathogen exposure that adversely impacted lung function.

Gastrointestinal disease

Seasonal variations also appear to impact a variety of gastrointestinal diseases. In a systematic review published in the Journal of Postgraduate Medicine, researchers analyzed seasonal and monthly data regarding the onset or relapse of acute pancreatitis, colon cancer, colonic diverticulitis, gastroesophageal reflux disease, and peptic ulcer. 

They found that peaks in peptic ulcer disease occurred during colder months, which could be due to seasonal changes in H. pylori infection. On the other hand, Crohn disease and acute appendicitis (in some countries) peaked in spring and summer. Seasonal variations in inflammatory bowel disease could be due to increased infection with intestinal bacteria, according to the authors. Lastly, seasonal variations in pancreatic enzyme secretion, as well as biliary acids and oxygen-free radicals, could underlie seasonal variations in acute pancreatitis. 

“However, our understanding of seasonality of diseases remains poor and will require a combination of experimental and observational studies,” they added. “Further understanding of the role of environmental factors (infection, cold, air pollution, etc) or other triggers (dietary habit, alcohol consumption) could be used to improve prevention measures and educational strategies, especially in people with the highest risk of gastrointestinal diseases.”

Reverse seasonal affective disorder

Clinicians are familiar with winter seasonal affective disorder, with symptoms including oversleeping, overeating, carbohydrate craving, and isolation. The converse of winter SAD is summer SAD, or reverse SAD, which is characterized by insomnia, lack of appetite, increased sex drive, and agitation. Both conditions are related to anxiety and depression, but winter SAD is better understood.

Although sun lamps to boost vitamin D production are often recommended for winter SAD, this intervention means little in summer when sunlight abounds. Instead, interventions for reverse SAD may include counseling, antidepressants, and lifestyle modifications. Finally, self-attack should be minimized, with thoughts of “everyone else is having a good summer and I’m not” quelled.

Suicide

One common myth is that people tend to commit suicide during the winter or holiday season. However, research shows that more suicides occur during spring and summer than in winter.

In a study published in Environmental Research, investigators examined the association between suicide attempts and temperature/humidity in residents of southern Israel. They found that suicide attempts during the summer season increased with every 5 °C increase in temperature. This link was stronger in those with psychiatric disorders and those who attempted suicide multiple times.

“High temperatures and low amount of precipitations are evidently of great impact on people's susceptibility to suicidal behavior, especially for individuals who have had a prior suicide attempt,” the researchers concluded. “Our findings indicate the need for public health attention in the summer when temperature increases precipitously over days, especially for those who have made a prior suicide attempt.”

Although it’s unclear why summer brings on suicide, experts have posed various hypotheses. For instance, biochemical changes in melatonin and other neurotransmitters may play a role. Additionally, mania may increase during the summer season. Even allergies have been suggested as playing a role, with their onset linked to higher levels of anxiety and social isolation. It could also be that more hours of daylight bring on increased activity, which manifests as suicide attempts.

Suicide is preventable. For more information, please contact the National Suicide Prevention Lifeline at 1-800-273-8255.