De Toni, L., Finocchi, F., Jawich, K., & Ferlin, A. (2023). Global warming and testis function: A challenging crosstalk in an equally challenging environmental scenario. Frontiers in cell and developmental biology. https://doi.org/10.3389/fcell.2022.1104326
De Toni L, Finocchi F, Jawich K, Ferlin A. Global warming and testis function: A challenging crosstalk in an equally challenging environmental scenario. Frontiers in cell and developmental biology. 2023. doi:10.3389/fcell.2022.1104326
De Toni, Luca, et al. "Global warming and testis function: A challenging crosstalk in an equally challenging environmental scenario." Frontiers in cell and developmental biology, 2023.
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Acute heat stress impairs sperm production, and most effects reverse
This review of animal and human studies finds that heat stress harms sperm production and testis hormones, and most of the harm reverses. Large studies of men link hot summers and temperature extremes to lower sperm counts. Proof that global warming is driving the long-term drop in sperm quality is still thin.
Study at a glance, narrative review of 4,874 men in Denizli, Turkey: Heat stress harms sperm production, and most effects reverse. Source: De Toni L et al., 2023, PMID 36726592.
Key Findings
Heat stress impaired sperm production and testis hormone production in animal and human models, and the review states most effects are reversible. Scrotal tissue runs 2°C–4°C below core body temperature.
Among 4,874 men in Denizli, Turkey, July and August showed significantly lower sperm concentration and total sperm count than December, May, or June.
In 10,802 men followed in Wuhan, China, every sperm measure was best at an ambient temperature of 13°C and declined almost linearly in either direction.
In 10 healthy men using a sauna twice a week for 3 months, sperm count and motility were strongly but reversibly impaired. Their serum sex hormones showed no significant change.
An 18-year analysis (1992–2010) found a yearly temperature rise of 0.09°C and significant declines in sperm concentration, total count, motile fraction, and normal-form fraction.
Interpretation
This is a narrative review. The authors bring together animal studies, studies of heat-exposed workers and sauna users, and seasonal studies of semen. The seasonal studies link warmer weather with lower sperm counts. A small sauna study found that sperm count and movement dropped, while hormone levels stayed steady. The authors note that proof linking rising global temperatures to falling sperm quality is still thin. The findings support larger, longer studies on climate warming and male fertility.
RRM Context
Restorative reproductive medicine checks both partners for causes that can be found and treated. This review adds one fact for the male exam: the testis works best below body temperature. The exposures it names include saunas, hot baths, long sitting, and heat at work.
Our editorial summary of this paper, not the article's abstract.
Abstract
Environmental pollution, accounting for both chemical and physical factors, is a major matter of concern due to its health consequences in both humans and animals. The release of greenhouse gases with the consequent increase in environmental temperature is acknowledged to have a major impact on the health of both animals and humans, in current and future generations. A large amount of evidence reports detrimental effects of acute heat stress on testis function, particularly on the spermatogenetic and steroidogenetic process, in both animal and human models, wich is largely related to the testis placement within the scrotal sac and outside the abdomen, warranting an overall scrotal temperature of 2°C-4°C lower than the core body temperature. This review will provide a thorough evaluation of environmental temperature's effect on testicular function. In particular, basic concepts of body thermoregulation will be discussed together with available data about the association between testis damage and heat stress exposure. In addition, the possible association between global warming and the secular decline of testis function will be critically evaluated in light of the available epidemiological studies.
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