Dr. Amir B. Saadi, an American physician and researcher of Iranian descent at Harvard Medical School, said: 'High nighttime temperatures can significantly degrade sleep quality,' stressing that his research with his team shows that hot nights lead to shorter sleep duration and disruption of its natural stages.

In an email interview with Asharq Al-Awsat, he added: 'Excessive heat causes frequent awakenings and a decrease in REM sleep, the stage important for dreams and emotional processing. This happens because the body struggles to dissipate heat. Normally, core body temperature drops at sleep onset as blood vessels dilate to release heat, but a hot environment hinders this cooling process. As a result, people take longer to fall asleep and experience fragmented, less restful sleep.'

He explained that poor sleep has serious consequences for mood, as insufficient or fragmented sleep is linked to bad mood and poor emotional control, stressing that studies have documented that short sleep duration is associated with an increased risk of depression and anger.

Dr. Amir B. Saadi, lecturer at Harvard Medical School and assistant researcher at the Marcus Institute for Aging Research (Asharq Al-Awsat)

B. Saadi led a research team and conducted a study in 2023, published in the journal 'Science of the Total Environment', which found that when temperatures rise from 25°C to 30°C, sleep efficiency decreases by up to 10 percent. According to the study results, this is not a trivial amount, as previous studies have shown that 'a 10 percent reduction in sleep efficiency is enough to impair brain performance and increase stress, anxiety, and fatigue,' and also affects 'blood sugar control during the following day.'

Hot Nights

B. Saadi said: 'In general, most adults sleep better in a cool environment with a temperature between 18 and 20°C. This range supports the body's natural temperature regulation and promotes REM sleep and deep sleep.'

He explained that older adults (65 and over) often need a warmer bedroom for restful sleep. With age, metabolic rate and core body temperature tend to decrease. Additionally, older adults physiologically have thinner skin and may suffer from poor circulation, so they feel cold more easily at night. One study found that sleep for adults over 65 is more comfortable when the bedroom temperature is between 21 and 23°C.

Regarding his advice for better, healthier sleep on hot nights, he said: 'There are many scientific strategies to keep the body cool and improve sleep. The first strategy is to keep the bedroom cool and well-ventilated. If you don't have air conditioning, a simple electric fan can circulate air over your skin, enhancing evaporative cooling.'

Older adults suffer greatly when sleeping on hot nights (Pixels)

He added that we should use lightweight, breathable bedding and sleepwear: by replacing bed sheets with light summer ones – such as cotton or linen – which allow airflow and absorb moisture. These materials allow sweat to evaporate and do not trap heat as much as synthetic fabrics.

He emphasized that taking a short lukewarm shower in the evening can lower your skin temperature. Even tepid water is effective – it causes vasodilation in the skin, releasing body heat, and can lead to a subsequent drop in internal body temperature, helping to initiate sleep easily.

B. Saadi emphasizes the need to drink plenty of water during the day and early evening to ensure proper hydration before sleep. Hydration helps regulate temperature through sweating, but he warns against drinking large amounts of water right before bed to avoid nighttime bathroom trips, saying that caffeine should also be avoided late in the afternoon or evening.

He urged that we regulate our sleep habits, as good sleep habits become more important when heat threatens our sleep. So we should maintain a regular sleep schedule, even if summer weather tempts us to stay up late. Going to bed and waking up at consistent times helps calibrate our biological clock, and we will be more likely to feel sleepy at bedtime.