During the summer months, it is common practice to protect oneself from the negative short-term effects of heat. We use sunscreen to shield our skin from UV rays that can cause sunburn. We drink fluids to maintain hydration. And we seek out shade to prevent heat illnesses such as heat exhaustion – a condition that occurs when the body overheats that typically results in heavy sweating, faintness or dizziness, and other symptoms such as headache and nausea. It is well-understood that heat can be dangerous in the short term – particularly for the very young, the elderly, or those that have fragile health.
It is less common that the general public is aware of the potential long-term health effects of repeated or prolonged heat exposure. This article seeks to provide information about what the health care profession currently understands about how extended exposure to heat can affect human health and well-being.
What is Heat Stress?
According to the University of Iowa’s Environmental Health & Safety Department, a condition called Heat Stress occurs when the human body cannot get rid of excess heat. High air temperatures, elevated humidity levels & strenuous activity all contribute to heat stress. Outdoor workers and athletes can be exposed to these conditions. It is also potentially true that indoor workers such as electricians or bakery / kitchen workers could have similar environmental stressors. Anyone that is consistently spending time in outdoor or indoor spaces in which temperatures are un-airconditioned are potentially at risk for heat stress. When a person’s body cannot cool down, early symptoms of heat stress might include rashes and cramps, or light-headedness, irritability, or difficulty concentrating. More extreme symptoms could include vomiting, fainting, or altered mental states such as confusion or delirium.
How Does the Human Body Cool Itself?
When the human body is exposed to heat, it attempts to cool itself in a variety of ways. Blood vessels in the skin dilate and blood is sent to the body’s surface to attempt to cool it down. Sweating also occurs, to cool the skin as this liquid evaporates. These systems of thermoregulation increase the workload of the heart and kidneys. The heart is required to pump harder & faster to compensate for the decreased blood pressure that occurs when blood vessels are dilated. And the kidneys, which filter waste from body fluids, are required to work harder when the body is dehydrated due to sweating. Typically, if a person is appropriately cooled in response to a Heat Stress response, their symptoms will fade and they will feel better. However, over time, repetitively or consistently excess stress to the heart and to the kidneys through extreme heat exposure can result in or exaggerate chronic disease within these organs.
What Are the Long-Term Effects of Heat Stress?
The cardiac and urinary body systems are not meant to function constantly in a high-stress mode. Cumulative effects of high-stress on the cardiac system include conditions like high blood pressure (HBP), abnormal heart rhythms, and increased oxygen demand by the heart to meet its need for additional energy to produce the increased heart rate that then drives blood circulation for a cooling response. Long-term effects of heat stress on the urinary system (which includes the kidneys) can include a gradual decline in kidney function or in some cases acute kidney injury, in which the kidneys may suddenly lose their capacity to filter waste products from the blood. According to the National Kidney Foundation, symptoms of acute kidney injury might include decreased production of urine, swelling in the legs / ankles / feet, and notable fatigue / tiredness. The Mayo Clinic indicates that chronic kidney decline is associated with similar symptoms, as well as possibly things like blood in the urine, itchy skin, & loss of appetite.
This article, published in the Washington Post in 2023, describes other ways that extended heat exposure can affect human health. The article describes a psychological effect of warmer temperatures – citing a study that correlates increased heat with increased mental-health related emergency visits. The article also discusses an association between hotter temperatures and decreased sleep quality and quantity. According to The Sleep Foundation, persistent sleep deficits negatively affect physical health in a variety of ways, with sleep-deprived persons at higher risk for conditions such as high blood pressure, obesity, and Type 2 diabetes.
According to the World Health Organization, approximately 489,000 heat-related deaths occur world wide each year! The Centers for Disease Control and Prevention (CDC) estimates that about 1200 people in the United States are killed by extreme heat annually. This number presumably primarily includes death related to acute heat-illness, such as cardiac events triggered by a heat wave. It is difficult to determine how many other deaths that occur over time are associated with prolonged or repeated heat stress. But it can be assumed that there are many.
How Can the Negative Effects of Prolonged Heat Exposure be Minimized?
In consideration of these sobering statistics, it makes sense to work as a community to prevent as many problems as possible related to heat exposure. So in addition to the short-term safety strategies of weathering a summer heat wave (such as drinking plenty of fluids and taking breaks from outdoor activity to cool down) what can be done to limit the risk of long-term health challenges associated with heat exposure? Here are several recommendations:
- In the short-term, educating oneself about strategies for Body Acclimatization to heat is worthwhile for those who are likely to be regularly exposed to heat. This graphic from the CDC explains steps that can be taken to gradually improving a body’s heat tolerance by working up over time to the amount of activity that one accomplishes in a hot environment.
- In the longer term and at a larger community level, additional useful heat protection strategies include:
- Increasing community access to air-conditioned spaces or cooling centers during hot weather. Policies and procedures that might help to achieve this access could include providing at-risk individuals with fans, portable air-conditioning units, or assistance in paying the costs of cooling, or facilitating transportation routes to libraries, community centers, or other cooled / shaded public spaces.
- Create shade via the planting of trees and by constructing structures such as tents or canopies in parks and recreation areas. Shade coverings reduce the amount of direct sunlight that hits the ground, reducing ground surface temperatures by as much as 30-40 degrees.
- Increase green spaces within urban areas that tend to hold heat. Human-made surfaces such as asphalt roadways retain heat during sunlight hours and then radiate this heat out at night. In contrast, plants and trees absorb solar energy and heat and the release water vapor, which cools the air around the plants. According to Vector Renewables, local air temperatures can be reduced by this process by up to 8-9 degrees.
For more information on heat-related human health topics, check out these resources:
The National Institute for Occupational Safety and Health: Heat Stress