"If you saw a heat wave, would you wave back?" - Steven Wright
My family moved to Maryland during a July heat wave that stretched for days with temperatures in the high 90’s and “feels like” temperatures of 100 to 105. When I took my two young children outside to play, we encountered a heavy wall of humidity that left us breathless. Having spent their short lives in the cooler conditions of New England, they lasted about 5 minutes before they begged to go back inside. The rest of the day was spent in a cramped apartment entertaining cranky and restless kids who were used to running around in the woods and digging in the dirt. It didn’t take long before my two happy children morphed into possessed and evil demons as each day of relentless heat made them miserable. Luckily, I discovered the county pool system, which for the next 15 years got my family through the DMV’s notoriously swampy summer season.
We are not at our best when we are physically uncomfortable, which for many in our area can be worse in the summer when the heat and humidity is oppressive. Recent studies suggest that heat may do more than just make us physically irritable as it can cause significant and measurable changes to our mental health. The effects of heat range in severity, from making us irritable to increasing the probability of experiencing an acute mental health crisis. Medical records from across the country show that of the more than 2.2 million adults who visited emergency rooms between 2010 and 2019, there was an 8 percent increase in visits for mental health crises during the hottest days of the summer. Incidences of self-harm, substance abuse, anxiety, mood disorders, and schizophrenia all rose in proportion to the heat, with these trends similar for both men and women of all ages across the U.S. Higher temperatures can also make certain disorders harder to manage, triggering relapses in people with bipolar disorder and increased deaths among those with schizophrenia and other mental health conditions.
Although we associate summer with relaxation, fun, and happy memories, science tells us otherwise. Survey data of close to 2 million Americans over a 15-year period shows that feelings of joy and happiness start to decrease as the temperature rises above 70 degrees. Negative emotions such as stress, anger, and fatigue are experienced more frequently on days with temperatures higher than 70 degrees than they are on days that range between 50 and 60 degrees. Our sense of well-being decreases as the temperature rises; as temperatures rise to the 90’s and above, joy and happiness diminish significantly while stress and anger dominate our emotional landscape. It seems our fond memories of happy, carefree summers may be a bit skewed; perhaps their glow has more to do with vacations and travel than summer weather. Temperatures between 50 and 60 degrees are the optimum breeding environment for positivity and stress management. It is harder to find our bliss in the heat of the summer.
Heat is a stressor, one that can reduce our resilience in ways that may fly under our emotional radar. When overheated, it is the body’s imperative to cool itself down, a process that not only takes a good deal of energy, but one that has the same physical characteristics as stress. Our heart beats faster and our breathing rate increases, becoming shallow and centered in the upper lobes of the lungs. Cortisol is released, mobilizing us into a “flight or fight” mode, diverting blood flow to the muscles and away from digestive processes. We become hyper-focused, tense, and on edge, very much like how we feel when agitated, angry, or stressed. Unless we are aware that our body is overheated, heat stress can masquerade as a feeling in search of a narrative. That’s why small disagreements that we would easily brush off can escalate into major offenses when we are hot and sweaty, or why a racing heart caused by dehydration can be misconstrued as anxiety or worry. Anyone who has ever attended a packed indoor cycling class with poor ventilation is sure to appreciate how the nicest people can become raging beasts when the fans aren’t turned on.
The old saying of being “hot and bothered” accurately describes how heat can influence our capacity to cope. Each of us has a certain baseline tolerance of stress. Provided we have adequate coping skills, we tend to stay within the parameters of our tolerance levels, or at least bounce back quickly when we are thrown off center. During times when our stress levels are approaching our baseline, when we are not feeling our best, or when our coping skills are compromised, heat can be the tipping point that pushes us beyond our limits, making daily annoyances feel overwhelming. When excessive heat extends over days and weeks, our stress tolerance decreases and we are more likely to feel more negative emotions, such as anger, agitation, and anxiety.
People with pre-existing mental health conditions may be especially vulnerable to the added stress of heat, which can be made worse by certain medications. High temperature exposure adversely impacts cognitive functioning, which may explain why heat waves are associated with increases in hospitalizations for dementia. Those who struggle with anxiety are particularly vulnerable to the physical stress of heat. The physical symptoms of being overheated—heart palpitations, nausea, shallow chest breathing, and dizziness--are similar to those of being anxious or can even mimic a panic attack. For those who struggle with anxiety, it can be especially hard to tease apart a mental health crisis from the purely physical symptom of being hot, especially when under stress.
Survey data shows that the link between heat and mental health is consistent around the world. This has scientists wondering whether heat does something to the brain. Research is looking at whether heat and long periods of oppressively hot weather might create an imbalance in brain signaling as previous studies have found disruptions in certain neurotransmitters during heat waves. Serotonin, dopamine, and noradrenaline are neurotransmitters that play a role in our moods, memory, and attention, but also play an important role in the regulation of body temperature. Scientists still do not know the precise pathways or roles played by these neurotransmitters, but their involvement explains why mental health suffers when the temperature rises.
There are also ongoing studies looking at whether exposure to heat can cause inflammation in the brain. The hypothalamus region of the brain is involved, among other processes, in body temperature regulation. Although it is difficult to study heat exposure and brain inflammation in humans, studies using rats have shown that a single exposure to oppressive heat leads to short-term neurological dysfunction which impacts attention, memory, and personality. Extrapolating data from rat studies to humans suggests that these inflammatory changes in the brain may impair our cognitive awareness of the environment and cause us to make poor decisions. This explains why someone who is extremely dehydrated and overheated may seem confused or disoriented, not actively seeking shade or refusing to drink water—two signs of an increased risk of heat stroke.
To date, the prominent theory of how heat impacts the brain is related to how it causes sleep disruptions. A large body of literature suggests that poor sleep is closely related to a decrease in our ability to cope and is linked to a worsening mental health status over time. Summertime, with its abundant daylight and warmer temperatures, creates conditions that are ripe for sleep disruptions. The extended exposure to sunlight in the summer suppresses melatonin, the hormone that is released as the sun starts to wane and is important in preparing the body for sleep. Additionally, our body temperature starts to drop a couple of degrees about an hour or two before bedtime and continues to drop while we are sleeping. This internal cooling is essential for the restorative, deep slow-wave phase of sleep. Without it, we find it harder to fall asleep and may wake up more frequently during the night. In the summer we tend to spend more time outside in the evening, prolonging our exposure to light and disrupting melatonin release. Even though oppressive heat may be less intense in the evening, temperatures above 70 degrees can delay the start of the body’s gradual cooling process and make it harder to initiate the internal cooling mechanisms that are necessary to get the shut-eye we need.
Throughout July we’ll look at how heat and the processes related to it—specifically, inflammation, sweating, and metabolism—help as well as hinder how well our body functions. Heat is an important source of transformation, one that triggers a number of bodily processes that are important to our immediate as well as long-term health and well-being. Like many other biochemical processes, when it comes to heat, the dose makes the poison and timing is everything. Importantly, we’ll explore the many myths related to heat that proliferate on social media, from how sweating gets rid of toxins, foods that supposedly speed up metabolism, and the various causes of inflammation. My hope is that you’ll gain a new appreciation and understanding of the role heat plays in the body as we slog through the humidity of our area’s swampy weather.
How does heat impact you? Can you sense the shift in your moods, cognition, or even your patience when you are overheated? What rituals do you follow when the days are longer and the temperature rises to be sure you get enough restorative sleep?