Air temperature anomalies on June 27th, 2021. Image: NASA

Welcome to our first climate and health literature review! This newsletter by the University of California Center for Climate, Health, and Equity will synthesize hot topics (no pun intended) in the world of climate and health to help you stay informed on clinically relevant literature.

In this first issue, we tackle the health impacts of heat. In the aftermath of the record-breaking heatwave that swept across the American West in late June, increasing ED visits for heat-related illness in the affected region by 69x and leading to around 600 deaths in Washington and Oregon, heat is on everyone's minds. In this issue, we'll be addressing the mechanisms by which heat harms the human body, how to protect yourself and your patients against its worse effects, and the equity issues at play.

So how does heat affect the body? Heat can directly lead to health effects by causing a range of heat-related illnesses described in the table below (spoiler alert: heatstroke is a medical emergency).

Image: Hemmelgarn & Gannon, 2013

But beyond heat-related illness, heat can lead to organ damage through a variety of mechanisms. One systematic synthesis identified five physiologic mechanisms affecting organs throughout the body: ischemia, heat cytotoxicity, inflammatory response, disseminated intravascular coagulation, and rhabdomyolysis. These mechanisms are implicated in increased risk of myocardial infarction 1-6 hours after heat exposure and a relatively new condition- chronic kidney disease of unknown cause sweeping across international agricultural communities. One study from JAMA found a statistically significant increase in hospitalizations among older adults on heat wave days for fluid and electrolyte disorders, renal failure, urinary tract infection, septicemia, and heat stroke. And some studies have shown that air pollution is increased during heatwaves, leading to synergistic negative effects on cardiovascular health in particular. Check out our Paper of the Week (more below) for a more detailed breakdown of the organ-system-specific changes in morbidity and mortality.

How do these organ effects and hospitalizations pan out? According to a recent study in Lancet Planetary Health, 0.91% of global excess deaths are heat-related, a number that has increased by 0.21 percentage points in the last 16 years. And a recent paper in Nature Climate Change estimates that, across the world, 37% of warm-season heat-related mortality is attributable to human-induced climate change. Without aggressive emissions reductions, the future looks bleak:

Image: NYTimes

But as the image depicts, adaptation can mitigate deaths. So while it doesn't seem like we will be escaping these heat waves anytime soon, read on to hear about how we can adapt as individuals, clinicians, and health systems.

Our paper of the week, a systematic review and meta-analysis, analyzes the effects of air temperature on mortality and morbidity outcomes among older adults.

Which patients are at highest risk of heat related morbidity and mortality? In one meta-analysis, prognostic factors significantly associated with highest risk of death during a heat wave were confinement to bed (OR 6.4), not leaving home daily (OR 3.4), being unable to care for oneself (OR 3.0), as well as preexisting psychiatric (OR 3.6), cardiovascular (OR 2.5), or pulmonary (OR 1.6) illness. Having working home AC, visiting cool environments, and increasing social contact were associated with better outcomes.

What evidence-based advice should we be giving patients? A Lancet review reported that the following commonly offered advice has a strong evidence base:

1. Increase fluid intake during hot weather: In particular, older adults should drink water without waiting for thirst due to a less strong thirst drive.

2. Stay in a cool or air-conditioned place: AC has been associated with a strong protective effect.

3. Wear light garments and shower/bathe frequently: Both activities had a clear exposure-response association in the 2003 Paris heatwave.

4. Restrict physical activity: Even a 3 degree C increase in core body temperature is dangerous.

5. Medication monitoring: Patients on drugs that can impede heat loss (see below) should be given recommendations on monitoring (e.g. bodyweight measurements).

In contrast, the following frequently touted advice is not well supported by evidence:

1. Use fans to stay cool: In fact, fans have not been associated with improvements in morbidity, likely because they increase the rate of dehydration.

2. Avoid alcohol and coffee: While alcohol does have a diuretic effect and can cause some degree of decreased heart contractility and peripheral vasodilation, low-moderate consumption of low-alcohol beverages (e.g. beer) and coffee/tea is probably okay. Spirits should be avoided.

There are limited studies specifically investigating drug use and heat-related morbidity, though there are some drug classes that are hypothesized to put patients at greater risk of poor outcomes after extreme heat exposure. Be cautious when prescribing the following drug classes during heat waves:

It's also important to counsel patients that the risks of certain recreational drugs may be higher during heat waves due to impaired alertness and perception of heat (e.g. opioids) and increased heat production (e.g. MDMA).

What can healthcare workers do? Talk to patients early (preferably spring and early summer) about common symptoms of heat-related illness and encourage them to seek out cooling facilities or public facilities like libraries if they do not have access to home AC. On a clinic/health system level, consider developing a system to check in with vulnerable patients during heat waves, or adopting a process for emergency recognition and management of heatstroke like the evidence-based heat alert pathway proposed by this study.

For more information, check out these excellent toolkits for patients, providers, and caregivers created by the Climate Psychiatry Alliance (available in multiple languages!).

As with everything in the climate change arena, there are some major equity issues at play when it comes to heat. It is well documented that low-wealth and communities of color are disproportionately affected by extreme heat. For example, according to one paper, those in low-wealth neighborhoods have significantly higher heat exposure compared to those in wealthier neighborhoods in the same city, and in 97% of American cities, the average person of color lives in an area with higher urban heat than non-Hispanic whites. This is due to the urban heat island effect, a phenomenon in which areas in cities with fewer trees and more paved surfaces that absorb and radiate heat (think asphalt) have warmer than average temperatures, sometimes by as much as 7 degrees C. And these variations are rooted in structural racism- in a study of over 100 American cities, one study shows that on a national scale, land surface temperatures in formerly redlined areas are about 2.6 °C hotter during the summer than in non-redlined areas, with significantly less tree cover.

Here's an image from an incredible NYTimes article summarizing the paper that shows the lingering effects of historical redlining in America's cities today: