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THOSE DARK SPOTS IN YOUR VISION? THEY'RE NOT "HARMLESS."
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| | Those dark spots floating across your vision?
Eye doctors call them harmless.
Turns out, they're not.
Floaters show up when the blood vessels in your eyes start collapsing. Oxygen stops reaching the cells that need it most. |  | | | | | | | If you'd rather not receive these emails, you can unsubscribe here. | |
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A Moderate Heat Wave Is Not Mild for Older Bodies A Lancet Planetary Health trial found three days of 34°C heat raised older adults' core temperature, heart rate and kidney stress markers. | | | The Capital Brief | October 03 | | | Climate & Health Edition | | A Moderate Heat Wave Is Not Mild for Older Bodies | | | | Heat warnings usually focus on extreme temperatures. A new trial suggests that for older adults, even a moderate heat wave puts measurable strain on the body. Researchers at the University of Ottawa published the study in The Lancet Planetary Health on September 30. In a climate chamber, 18 adults aged 67 to 84 each spent three days in a simulated heat wave, 34°C during the day and 26°C at night, and, on a separate occasion, three days at a constant 26°C. The design let each person serve as their own comparison, and researchers tracked core temperature, heart function, blood pressure, blood markers of organ stress, balance and attention. During the heat wave, daily peak core body temperature was 0.4°C higher on average, and it rose again every day rather than adapting. Heart rate was higher, blood pressure on standing dropped more, and markers of kidney and gut stress increased. Balance and attention were also worse. The study was small and conducted in healthy volunteers in a controlled chamber, without the fans, cool showers or air conditioning people might use at home. It measured physiological strain, not heat illness or hospital admissions. The useful idea is that protection from heat should start at moderate temperatures for older adults, not only during extreme events. This edition explores the evidence, not individual medical advice. Signs of heat illness, such as confusion, fainting or a very high body temperature, require emergency care. | | 01 | Why older adults are more vulnerable | | | As people age, the body becomes less efficient at shedding heat. Sweating declines, and the ability to send blood to the skin to release heat is reduced. The heart has to work harder to cool the body, which can strain people with heart disease. Many common medicines, including some for blood pressure and mood, can affect fluid balance or heat tolerance. Older adults may also feel thirst less strongly and may not notice they are overheating. Heat waves are consistently associated with increases in deaths and hospital visits among older people. Understanding the physiology helps explain why. | | 02 | How the trial was designed | | | Participants were recruited from the Ottawa-Gatineau region, with a median age of 74 and an equal number of women and men. Each completed both conditions in random order: three days of simulated heat wave and three days at 26°C. Humidity was held at 45%, and participants remained in the chamber with limited physical activity. Researchers measured core temperature continuously and collected heart, blood pressure, blood, balance and cognitive data. The crossover design reduces the influence of differences between people, because each person is compared with themselves. The trial was funded by Health Canada and the Canadian Institutes of Health Research, and the authors reported no competing interests. No adverse events occurred during the trial. | | 03 | Body temperature stayed high | | | Daily peak core temperature averaged 37.8°C during the heat wave, compared with 37.4°C in the control condition. The difference of 0.4°C was consistent and statistically significant. Importantly, the elevation recurred each day. Participants did not adapt over the three days. Warm nights at 26°C did not provide enough relief to reset the body for the next day. A rise of less than half a degree may sound small, but it reflects sustained strain on cooling systems. In real heat waves lasting longer, or with higher temperatures, that strain could accumulate. The finding supports cooling strategies that address both daytime heat and warm nights. | | 04 | The heart and blood pressure | | | Heart rate was about 5 beats per minute higher on average during the heat wave, and about 8 beats higher at the end of the day. Blood pressure dropped substantially more when participants stood up, by about 27 millimeters of mercury systolic in the heat. That kind of drop can cause dizziness or lightheadedness, which may raise the risk of falls. Measures of heart rhythm variability suggested reduced control of the heart by the nervous system. These changes indicate the cardiovascular system was working harder to manage heat. For people with heart disease, that additional workload can be risky. The study did not measure heart attacks or other clinical events. | | 05 | Kidneys, gut, balance and attention | | | A blood marker of kidney stress, NGAL, rose during the heat wave and remained elevated the next morning. A marker of gut injury, I-FABP, also increased. Balance worsened, with lower scores on a standing balance test. Attention, measured by a cognitive test, declined on the second and third days of heat. Participants drank more fluids in the heat, but their overall fluid balance did not differ between conditions. These findings suggest heat affects multiple body systems, not only temperature regulation. Short-term biomarker changes do not prove lasting damage, but they signal stress. | | | | With only 18 participants, the study is small, and results may not apply to everyone. Participants were healthy enough to complete a chamber study, so the frailest older adults were likely not included. They could not use personal cooling strategies such as fans, cool showers or air conditioning. Chamber conditions were constant, unlike real weather, and physical activity was restricted. The trial measured physiological and biomarker changes, not heat illness, hospitalizations or deaths. Race and ethnicity data were not collected. These limits make the findings a strong signal, not a precise prediction for every person. | | 07 | What older adults and families can do | | | Treat moderate heat seriously, not only heat-wave warnings with extreme temperatures. Spend time in air-conditioned spaces when possible, including public cooling centers, libraries or malls. Cool showers, wet cloths and fans in moderate conditions can help, though fans alone may be less effective in very high heat. Drink fluids regularly, and ask a clinician whether any medicines affect heat tolerance or fluid needs. Stand up slowly, especially in heat, to reduce dizziness and fall risk. Families and neighbors can check on older adults during hot periods, especially those living alone. Know the signs of heat illness, including confusion, fainting, nausea and very hot skin, and call 911 if they appear. | | 08 | The long view on heat and health | | | As heat waves become more frequent and longer, more older adults will face repeated exposure. This trial suggests the body does not simply adapt over a few days, and warm nights do not provide full recovery. For individuals, the practical questions are: Where can I cool off? Do my medicines affect heat tolerance? Who will check on me during a heat wave? For communities, cooling centers, outreach programs and heat-health warning systems can reduce risk. For housing and building policy, access to cooling is increasingly a health issue. The long-view idea is that heat risk for older adults begins earlier than many warnings suggest. Staying cool is not comfort. For aging bodies, it is protection. | | | | The Takeaway | | 1 | In a randomized crossover trial, a three-day moderate heat wave raised older adults' daily peak core temperature by about 0.4°C. | | 2 | The temperature rise recurred each day, and warm nights did not reset it. | | 3 | Heart rate rose, blood pressure dropped more on standing, and kidney and gut stress markers increased. | | 4 | The study was small and measured physiological strain, not heat illness or deaths. | | 5 | Older adults benefit from cooling strategies during moderate heat, not only extreme heat waves. | | | Stay patient, stay curious,
T.C. Brown
Editor, True Capital Talk | | | | Sources & Further Reading | | | | For educational and informational purposes only. Nothing here is a diagnosis or individualized medical advice. Signs of heat illness such as confusion, fainting or very high body temperature require emergency care; call 911. Talk to a clinician about how medicines affect heat tolerance. | | |
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