Seasonal Variation in Serum T3 and T4 Levels in Man.

Smals, A. G. H.; Ross, H. Alec; Kloppenborg, P. W. C.

doi:10.1210/jcem-44-5-998

Cited by 69 publications

(29 citation statements)

References 15 publications

(11 reference statements)

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“…These results suggest that variations of external temperature are not very important in determining basal TSH levels in euthyroid subjects, in contrast with a pre vious finding in patients with primary hypothyroidism treated with constant doses of L-T4: in such patients, Konno and Morikawa [3] have described a TSH hyper secretion in winter, significantly related to the lowering of ambient temperature. However, the plasma TSH ele vation in winter in hypothyroid patients could be related to insufficient T4 replacement during the cold season, since the effect of the cold exposure on thyroid function in man is probably mediated by an increased rate in the peripheral metabolism of thyroxine [ 15], and the TSH response to thyrotropin releasing hormone does not change throughout the year [16], Thus, changes in am bient temperature might act as a synchronizer, rather than as a real cause of the TSH circannual rhythm.…”

Section: Discussionmentioning

confidence: 99%

Circannual Rhythm of Plasma Thyrotropin in Middle-Aged and Old Euthyroid Subjects

et al. 1990

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The circannual rhythm of plasma thyrotropin (TSH) was evaluated in 8,310 euthyroid, serially independent, young, middle-aged and old men and women. A statistically significant circannual rhythm of plasma TSH was validated, by the mean group-cosinor method, in the middle-aged and old men and women (p < 0.05), with acrophase in December, whereas the young subjects did not show any rhythm. No significant correlation was found between TSH plasma levels and free thyroxine (fT₄) or ambient temperature in any group. Moreover, plasma fT₄ did not show seasonal variations.

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Section: Discussionmentioning

confidence: 99%

Circannual Rhythm of Plasma Thyrotropin in Middle-Aged and Old Euthyroid Subjects

et al. 1990

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“…Research by Leonard and colleagues (1999) demonstrated a link between free thyroxine levels and metabolic variation in indigenous Siberians during a single seasonal period (i.e., the late summer). Other researchers have demonstrated seasonal fluctuations in thyroid hormones in indigenous and non-indigenous high-latitude populations, which appear to be the related to variation in temperature and photoperiod (Osiba, 1957;Eastman et al, 1974;Smals et al, 1977;Tkachev et al, 1991;Bojko, 1997;Hassi et al, 2001).…”

mentioning

confidence: 95%

Basal metabolic rate in the Yakut (Sakha) of Siberia

et al. 2005

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Human indigenous circumpolar populations have elevated basal metabolic rates (BMRs) relative to predicted values; this metabolic elevation has been postulated to be a physiological adaptation to chronic and severe cold stress. The present study examines BMR in the Yakut, an indigenous high-latitude population from the Sakha Republic of Russia to determine (1) whether the Yakut show evidence of an elevated BMR, (2) if the Yakut display evidence of age-related changes in BMR, and (3) whether lifestyle differences influence BMR. BMR was measured during the late summer in 75 women and 50 men (ages 18-56 years) from the Siberian village of Berdygestiakh. Measured BMR (+/- SEM) of the entire sample was significantly elevated (+6.5%) compared to predictions based on body mass (6,623.7 +/- 94.9 vs. 6,218.2 +/- 84.7 kJ/day; P < 0.001). Additionally, measured BMR for the entire sample was significantly higher than predictions based on fat-free mass (+20.8%) and surface area (+8.9%). Males and females both showed significant elevations relative to all three standards. The elevated BMR of the Yakut does not appear to be attributable to extreme levels of protein, since the Yakut consume a mixed diet with a substantial proportion of carbohydrates. No significant age-related changes in BMR were found when controlled for body composition. No significant relationship was found between lifestyle variables and BMR, suggesting the possibility of a genetic or developmental mechanism. This study provides additional evidence of metabolic elevation in indigenous circumpolar groups and has important implications for estimating the nutritional requirements of these populations.

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“…Japanese subjects living in unheated dwellings had higher serum total triiodothyronine (T 3 ) levels in winter than in summer, but subjects working outdoors showed no differences in serum T 3 or thyroxine (T 4 ) between summer and winter (Nagata et al 1976). High serum total T 3 and T 4 levels in winter were also found in laboratory workers in the Netherlands (Smals et al 1977) and the UK (Harrop et al 1985). This would indicate that the pituitary-thyroid axis becomes directly activated during the cold season.…”

Section: Introductionmentioning

confidence: 99%

The pituitary-thyroid axis in healthy men living under subarctic climatological conditions

Hassi

Sikkilä²,

Ruokonen³

et al. 2001

Journal of Endocrinology

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In order to evaluate the effects of climatic factors on the secretion of thyroid hormones and TSH in a high latitude population, we have taken serum and urine samples from 20 healthy men from northern Finland (67 -68 N) every 2 months for a period of 14 months. Serum free triiodothyronine (T 3 ) levels were lower in February than in August (3·9 vs 4·4 pmol/l, P<0·05) and TSH levels were higher in December than during other months (2·1 vs 1·5-1·7 mU/l, P<0·01). Serum total and free thyroxine (T 4 ), total T 3 and reverse T 3 levels and urinary T 4 levels were unchanged. Urinary T 3 levels were significantly higher in winter than in summer. Serum free T 3 correlated highly significantly with the outdoor temperature integrated backwards weekly for 7-56 days (r=0·26 for 1-56 days) from the day when the blood samples were taken. Serum TSH did not show any significant correlation with the thyroid hormones or with the integrated temperature of the previous days, but it did show an inverse and significant correlation (r= 0·31) with the ambient luminosity integrated backwards for 7 days from the day when the blood sample was taken. The gradually increasing correlation between outdoor temperatures and serum free T 3 suggests that the disposal of thyroid hormones is accelerated in winter, leading to low serum free T 3 levels and a high urinary free T 3 excretion. Since there was no correlation between thyroid hormones and serum TSH, the feedback mechanism between TSH and thyroid hormones may not be the only contributing factor, and other factors such as ambient luminosity may at least partly determine serum TSH in these conditions. Also urinary free T 3 appears to be a novel and non-invasive indicator for thyroid physiology.

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Seasonal Variation in Serum T3 and T4 Levels in Man.

Cited by 69 publications

References 15 publications

Circannual Rhythm of Plasma Thyrotropin in Middle-Aged and Old Euthyroid Subjects

Circannual Rhythm of Plasma Thyrotropin in Middle-Aged and Old Euthyroid Subjects

Basal metabolic rate in the Yakut (Sakha) of Siberia

The pituitary-thyroid axis in healthy men living under subarctic climatological conditions

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