KUALA LUMPUR, Aug 26 — A recent study by scientists from Singapore and the United Kingdom have found evidence that high temperatures impact human hormone levels and their endocrine system.
The recent review, covering studies since the 1940s, indicates that heat impacts hormone production and function, increased the risk of gestational diabetes and thyroid disorders in pregnant women, and sperm count in men.
“Basically we know the impacts, but the ‘why’ and ‘how’ are lacking,” Jason Le, an associate professor from the Yong Loo Lin School of Medicine in the National University of Singapore (NUS) told Singapore’s Straits Times (ST) in an article published yesterday.
Hormones, which regulate numerous bodily functions, can be disrupted by extreme heat, potentially leading to health issues such as blood sugar imbalances and reproductive problems.
A separate study from the US in 2017 found that higher temperatures could affect glucose metabolism, thus increasing the risk of diabetes.
Lee, who is also the director of the Heat Resilience and Performance Centre at NUS Medicine, said exposure to high heat also poses a higher risk of premature birth, low birth weight, and stillbirth.
This could be due to inflammation and reduced blood flow to the uterus, as the body diverts blood to the skin to cool down.
Lee, who is leading a South-east Asian research programme called Project HeatSafe, said the impact on fertility is well-documented, with elevated temperatures known to reduce sperm count and affect women’s ovulation cycles.
He added that there is yet no direct link between extreme heat and gestational diabetes among Singaporean women, likely due to protective measures like air conditioning.
But men exposed to temperatures above 29.8°C had a 46 per cent higher risk of low sperm count.
Lee stressed that avoiding extreme heat is crucial as the exact temperature benchmark is not currently known, adding that more research is needed to understand these mechanisms.
Patients with endocrine disorders such as diabetes and hyperthyroidism face a higher risk of heat-related illnesses, which could strain the healthcare system.
The study also highlights the need for further investigation into the long-term effects of heat on the endocrine system in the context of climate change.
Fadil Hannan from the University of Oxford, the lead author of the study, noted the limited knowledge about how increased heat exposure due to climate change might affect endocrine health.
“We know very little about whether increased heat exposure due to climate change could affect endocrine health,” Hannan was quoted as saying by ST.
Fadil is also involved in a study in India aiming to explore how extreme heat affects pregnancy and lactation, with the goal of developing protective policies.
Published in Nature Reviews Endocrinology on July 30, the study suggests that early exposure to high temperatures might have adverse effects on child health.
Experiments involving pregnant rats exposed to 43°C for 15 minutes showed offspring with brain malformations linked to reduced adrenal gland size.
Melvin Leow from Singapore’s Tan Tock Seng Hospital explained that heat stress could lead to increased steroid circulation, affecting glucose production and insulin resistance.
“This might just be one of the postulated pathways to the increased odds of developing diabetes, but it will take more human studies to determine and quantify the magnitude of this risk,” he was quoted as saying.