Arquivo da tag: Hormônios

Study of 3.5 Million People Finds Human Hormones Change With The Seasons (Science Alert)

Carly Cassella, 7 FEBRUARY 2021

A review of millions of blood tests has shown a whole host of human hormones that fall into clear seasonal patterns, although these changes are small in magnitude.

Hormones from the pituitary gland, which help control reproduction, metabolism, stress and lactation, were mostly found to peak in late summer.

Peripheral organs under the control of the pituitary, like those that produce our sex hormones or the thyroid hormone, also showed seasonality. Instead of peaking in summer, however, these hormones hit their stride in winter.

Testosterone, estradiol, and progesterone, for instance, reached their pinnacle in late winter or spring.

The findings provide the strongest evidence to date that humans possess an internal seasonal clock, which somehow impacts our hormones in a way that lines up with the seasons.

“Together with a long history of studies on a winter−spring peak in human function and growth, the hormone seasonality indicates that, like other animals, humans may have a physiological peak season for basic biological functions,” the authors write

The underlying mechanism that drives this circannual clock is still unknown, but the authors suggest there is a natural, year-long feedback circuit at play between the pituitary gland and peripheral glands in the body.

The pituitary hormones, which are uniquely tuned to sunlight, could be feeding these other organs over the course of a year, allowing them to grow in functional mass in a way that aligns with the seasons.

“Thus, humans may show coordinated seasonal set-points with a winter−spring peak in the growth, stress, metabolism, and reproduction axes,” the authors write.

As the paper mentions, it’s not too different from what we find in other mammals, where fluctuations in certain hormones lead to seasonal changes in an animal’s reproduction, activity, growth, pigmentation, or migration.

Mammals like arctic reindeer, for instance, show a decrease in a hormone called leptin when winter days become shortest, and this helps lower their energy consumption, decreasing their body temperature and inhibiting their ability to reproduce.

Even primates closer to the equator show sensitivity to subtle seasonal changes. For instance, Rhesus macaques ovulate significantly more during the post-monsoon season so that their offspring are born just before the monsoons hit in summer.

Whether or not human hormones also fluctuate with the seasons remains unclear.

Most datasets that have been analysed so far are not very large and do not cover all human hormones, which makes drawing conclusions very challenging. Studies have either examined only human sex hormones, or they have focused on stress and metabolic hormones. Results have also been quite varied and inconsistent.

While some studies on human sex hormones suggest seasonal changes should be considered, other studies conclude seasons are an unimportant source of variability. 

Meanwhile, research on salivary cortisol levels – aka the stress hormone – finds there is some seasonal variability, and a big data study on the thyroid-stimulating hormone found higher levels of this hormone in summer and winter.

The new research is the largest of the lot and includes a massive dataset of Israeli health records covering 46 million person-years. It also analyses all human hormones.

Controlling for changes throughout a single day, the authors found humans do show seasonal patterns in their hormone levels, although not as strongly as other mammals.

The physiological effects of these hormonal shifts are still not clear, but some of the changes to the thyroid hormone, T3, and the stress hormone, cortisol, do align with previous findings.

For example, the thyroid hormone, which was found to peak in winter, has been tied to thermogeneration.  The seasonal timing of cortisol, which was found to peak in February, also agrees with past studies spanning the northern and southern hemispheres.

The seasonal changes are small in magnitude, but as the authors point out, from a clinical perspective, “even a small systematic effect can cause misdiagnosis if the normal ranges are not adapted to the seasons, with associated costs of extra tests and treatment.”

More studies on a similarly large scale and in various parts of the world will need to be done to verify the results further. But the findings suggest we are not so different from other mammals after all.

If our hormones really do ebb and flow with the seasons, even just a little bit, it could be important for our health that we know. 

The study was published in PNAS.

Fetal Exposure to Excessive Stress Hormones in the Womb Linked to Adult Mood Disorders (Science Daily)

Apr. 6, 2013 — Exposure of the developing fetus to excessive levels of stress hormones in the womb can cause mood disorders in later life and now, for the first time, researchers have found a mechanism that may underpin this process, according to research presented April 7 at the British Neuroscience Association Festival of Neuroscience (BNA2013) in London.

(Credit: © Tatyana Gladskih / Fotolia)

The concept of fetal programming of adult disease, whereby the environment experienced in the womb can have profound long-lasting consequences on health and risk of disease in later life, is well known; however, the process that drives this is unclear. Professor Megan Holmes, a neuroendocrinologist from the University of Edinburgh/British Heart Foundation Centre for Cardiovascular Science in Scotland (UK), will say: “During our research we have identified the enzyme 11ß-HSD2 which we believe plays a key role in the process of fetal programming.”

Adverse environments experienced while in the womb, such as in cases of stress, bereavement or abuse, will increase levels of glucocorticoids in the mother, which may harm the growing baby. Glucocorticoids are naturally produced hormones and they are also known as stress hormones because of their role in the stress response.

“The stress hormone cortisol may be a key factor in programming the fetus, baby or child to be at risk of disease in later life. Cortisol causes reduced growth and modifies the timing of tissue development as well as having long lasting effects on gene expression,” she will say.

Prof Holmes will describe how her research has identified an enzyme called 11ß-HSD2 (11beta-hydroxysteroid dehydrogenase type 2) that breaks down the stress hormone cortisol to an inactive form, before it can cause any harm to the developing fetus. The enzyme 11ß-HSD2 is present in the placenta and the developing fetal brain where it is thought to act as a shield to protect against the harmful actions of cortisol.

Prof Holmes and her colleagues developed genetically modified mice that lacked 11ß-HSD2 in order to determine the role of the enzyme in the placenta and fetal brain. “In mice lacking the enzyme 11ß-HSD2, fetuses were exposed to high levels of stress hormones and, as a consequence, these mice exhibited reduced fetal growth and went on to show programmed mood disorders in later life. We also found that the placentas from these mice were smaller and did not transport nutrients efficiently across to the developing fetus. This too could contribute to the harmful consequences of increased stress hormone exposure on the fetus and suggests that the placental 11ß-HSD2 shield is the most important barrier.

“However, preliminary new data show that with the loss of the 11ß-HSD2 protective barrier solely in the brain, programming of the developing fetus still occurs, and, therefore, this raises questions about how dominant a role is played by the placental 11ß-HSD2 barrier. This research is currently ongoing and we cannot draw any firm conclusions yet.

“Determining the exact molecular and cellular mechanisms that drive fetal programming will help us identify potential therapeutic targets that can be used to reverse the deleterious consequences on mood disorders. In the future, we hope to explore the potential of these targets in studies in humans,” she will say.

Prof Holmes hopes that her research will make healthcare workers more aware of the fact that children exposed to an adverse environment, be it abuse, malnutrition, or bereavement, are at an increased risk of mood disorders in later life and the children should be carefully monitored and supported to prevent this from happening.

In addition, the potential effects of excessive levels of stress hormones on the developing fetus are also of relevance to individuals involved in antenatal care. Within the past 20 years, the majority of women at risk of premature delivery have been given synthetic glucocorticoids to accelerate fetal lung development to allow the premature babies to survive early birth.

“While this glucocorticoid treatment is essential, the dose, number of treatments and the drug used, have to be carefully monitored to ensure that the minimum effective therapy is used, as it may set the stage for effects later in the child’s life,” Prof Holmes will say.

Puberty is another sensitive time of development and stress experienced at this time can also be involved in programming adult mood disorders. Prof Holmes and her colleagues have found evidence from imaging studies in rats that stress in early teenage years could affect mood and emotional behaviour via changes in the brain’s neural networks associated with emotional processing.

The researchers used fMRI (Functional Magnetic Resonance Imaging) to see which pathways in the brain were affected when stressed, peripubertal rats responded to a specific learned task. [1].

Prof Holmes will say: “We showed that in stressed ‘teenage’ rats, the part of the brain region involved in emotion and fear (known as amygdala) was activated in an exaggerated fashion when compared to controls. The results from this study clearly showed that altered emotional processing occurs in the amygdala in response to stress during this crucial period of development.”

Abstract title: “Perinatal programming of stress-related behaviour by glucocorticoids.” Symposium: “Early life stress and its long-term effects — experimental studies.”

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The above story is reprinted from materials provided byBritish Neuroscience Association, via AlphaGalileo.