ARKHANGELSK, February 16. /TASS/. Scientists of the Laverov Federal Research Center for Integrated Arctic Studies (Arkhangelsk, the Urals Branch of the Russian Academy of Sciences) identified a difference in reactivity of thyroid hormones and dopamine in men and in women who live in Russia's European North. Having analyzed thyroid hormone levels depending on seasons, they found that women are better adapted to adverse climatic conditions, leader of the Tkachev Laboratory of Endocrinology at the Institute of Physiology of Natural Adaptations, Doctor of Biological Sciences Elena Tipisova told TASS.
"In low-light conditions, are produced big amounts of melatonin, a hormone responsible for circadian rhythms. Melatonin inhibits the activity of both the thyroid gland and the production of dopamine. Winter is the most stressful season for the human body. We have found that men and women react to winter differently. Women were more labile. With different levels of dopamine in women, their thyroid activity increased in winter anyway. In men, thyroid activity remained low in winter, like it was in autumn. It turns out that women are more adapted to adverse climatic conditions," the scientist said.
Thyroid hormones' levels in northerners begin to decrease in autumn, and this trend continues in winter, experts said. Photoperiodism plays a key role in this process. Over the research, physiologists have confirmed that both in autumn and winter, the thyroid gland activity in women in the North is higher than in men. At the same time, thyroid diseases are more common in women (which corresponds to world statistics). Fluctuations in levels of thyroid hormones' free fractions were observed in women. In men, they were stable throughout all seasons of the year. In other seasons, men and women in the North reacted almost the same way: in spring and summer, they had equally high concentrations of thyroid hormones.
Dopamine and thyroid gland
In some of the examined men, specialists have found an increase in thyroid hormones level against the background of an increase in dopamine, the so-called hormone of joy. The dopamine levels' decrease was accompanied by a thyroid hormones' decrease.
"Even with relatively low dopamine levels, women still had increased thyroid activity in winter. We believe that some other mechanisms are involved here and they stimulate the thyroid hormones production. One of indicators that we were able to trace is an increase in cortisol levels. According to our colleagues, cortisol also can be combined with an increase in the conversion of thyroxine (T4) into the more active triiodothyronine (T3). Usually, when dopamine rises, cortisol decreases: mood increases and stress decreases. And vice versa-when dopamine decreases, joy decreases, and the stress hormone cortisol increases. However, we have seen opposite reactions, where, perhaps, cortisol compensated for the effect of dopamine by converting thyroxine into triiodothyronine," the scientist said.
This explains partly why women are more adapted to the North's adverse climatic conditions. This type of adaptive reactions may be associated with childbirth: the mother's body needs to get adapted intensively to negative factors.
Seasonal depressive disorders often occur in autumn, when, in lower air temperature and shorter daylight, happens a decrease in dopamine levels and also a decrease in the thyroid gland activity. A decrease in the thyroid gland activity in autumn may be associated with a decrease in metabolic processes and the body's preparation for winter, like it happens in some animals.
The norms of endocrine and metabolic regulation for the North's residents can often differ from similar indicators for residents of more southern territories due to the influence of temperature and photoperiods. Earlier, it was Arkhangelsk's physiologist Anatoly Tkachev (1936-2005) who came up with this concept.
In Northerners, a common adaptive reaction to extreme environmental conditions is an increased activity of the thyroid gland with increased levels of thyroid hormones that regulate metabolism, growth, tissue development, heart and nervous system functions. In addition, thyroid hormones can absorb free radicals, the body's unstable molecules that damage DNA, and thus prevent premature aging and the body destruction. However, in recent decades, due to climate warming and changes in the social lifestyle, we can see a slight decrease in thyroid activity.
The North is also known for a "low T3 syndrome" with low values of triiodothyronine (T3), which is associated with the risk of developing various somatic diseases. "We have identified low T3 values in 65% of men and in 30% of women, which was especially pronounced in autumn and winter periods. Due to the significant role of thyroid hormones in the body, low triiodothyronine levels may be risk criteria for developing maladaptation to the North's conditions, for reducing the body's reserve capabilities," the expert added.
Further on, the center's specialists will study how sex hormone levels in men and women are changing in different seasons.