Heat disrupts hormones and delays menstrual cycle, doctors say

December marks the start of the hottest period of the year and highlights a little-discussed but increasingly obvious effect: the direct impact of high temperatures on hormonal balance.

With heat waves more frequent in Brazil, the body begins to function in a continuous effort to stay safe, and this mechanism affects everything from mood to the menstrual cycle.

Heat not only affects the feeling of physical discomfort: it modifies the internal processes that support the functioning of hormones. Endocrinologist Fernanda Parra explains that in extreme heat, the body goes into adaptation mode.

“Excessive heat activates the body’s survival mechanisms, increasing stress hormones such as cortisol. Most people experience this as irritability, fatigue or difficulty sleeping, but they rarely associate it with the weather,” he says. The increase in cortisol, she says, is an automatic response, but can generate persistent symptoms when the heat continues.

How heat changes hormonal functioning

When the body is confronted with very high temperatures, it interprets the heat as a stressor. This causes an increase in cortisol and, at the same time, reduces the production of the thyroid hormones T3 and T4 to save energy.

The person may feel lethargic, sleepy, slow down at work and have difficulty concentrating. Parra points out that these fluctuations are real, even when hormone tests remain within normal limits.

Common summer dehydration makes the situation worse: with less fluid circulating, hormone transport is impaired. This helps explain episodes of dizziness, weakness, excessive fatigue and a feeling of mental exhaustion.

In women, the effects of heat become much more noticeable. Gynecologist Alexandre Pupo Nogueira points out that high temperature does not directly modify the secretion of estrogen and progesterone, but that heat stress and excess cortisol can influence ovulation and the menstrual cycle.

“Increased cortisol can affect the secretion of gonadotropins — FSH and LH — which regulate the functioning of the ovaries. This can alter the ovulatory period, cause menstrual delays and change the bleeding pattern,” he explains.

Pupo also points out that dehydration can indirectly interfere with the cycle. When the body loses water, the metabolism goes into alert, altering the release of hormones that regulate the menstrual cycle. “It is common that this causes delays, in addition to worsening irritability and mood changes,” explains the doctor.

Important care for women in summer

To reduce the hormonal impacts of heat, experts recommend:

Constant hydrationincluding electrolyte drinks, to maintain stable hormonal transport.
Avoid the sun between 10 a.m. and 4 p.m. when there is a greater risk of heat stress.
Light clothing and natural fabricslike cotton and linen, which help dissipate heat.
Sleep regularly, go to bed earlier to minimize sleepless nights caused by heat.
Light diet, favoring fruitsvegetables and fresh foods.
Ventilated environments or with adequate ventilation, reducing thermal overload.
Avoid strenuous exercise during hotter periodsprotecting the body from cortisol peaks.

Who feels it most: impact on pre-existing hormonal diseases

Certain conditions make the body even more sensitive to heat. Women with polycystic ovary syndrome (PCOS), for example, already live with chronic inflammation and insulin resistance. According to Pupo, heat stress increases both, which can worsen symptoms like acne, menstrual irregularities, and excess hair.

In endometriosis, a condition that also involves systemic inflammation, high cortisol levels intensifies sensitivity to pain. In the event of thyroid dysfunction, the impact is twofold:

In hypothyroidismthe combination of a slow metabolism and high cortisol levels increases fatigue.
In hyperthyroidism, The accelerated metabolism produces even more internal heat, making external heat waves particularly exhausting.

Changes such as hyperthermia, severe headache, dizziness, failure to urinate, swelling, palpitations, and extreme exhaustion are warning signs and require medical evaluation. In the case of the menstrual cycle, delays of more than 10 days, very heavy periods or the absence of periods for two months also require investigation.

Emotional changes – such as irritability, increased sensitivity and difficulty controlling stress – are common in hot weather, particularly because sleep tends to become lighter and more fragmented. This reduces the body’s ability to regulate hormones essential for mood and the ovulatory cycle.

For Parra, recognizing that climate influences the endocrine system is fundamental. “The endocrine system is sensitive to the environment. Taking care of your body in hot weather is a way of protecting your hormonal balance,” he explains.

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