title: Seasonal variation in basal metabolic rates among the Yakut (Sakha) of Northeastern Siberia.
abstract: OBJECTIVE
  Previous research has shown that indigenous circumpolar populations have elevated basal metabolic rates (BMRs), yet few studies have explored whether metabolic rates increase during the winter. This study addresses this gap by examining seasonal variation in BMR and its associations with thyroid function and lifestyle factors among the Yakut (Sakha) of Siberia.
  
  
  METHODS
  Anthropometric dimensions, BMR, and thyroid hormone levels (free triiodothyronine [fT3], free thyroxine [fT4], thyroid-stimulating hormone [TSH]) were measured on two occasions (July/August, 2009 and January 2011) on a sample of 94 Yakut (Sakha) adults (35 men, 59 women) from the rural village of Berdygestiakh, Sakha Republic, Russia.
  
  
  RESULTS
  Seasonal changes in BMR varied by age. Younger Yakut adults (19-49 years) showed significant elevations in winter-time BMR of 6% (P < 0.05), whereas older individuals (≥50 years) showed modest declines (2%; n.s.). Both younger and older Yakut men and women showed increased respiratory quotients during the winter. FT3 and fT4 levels significantly declined during the winter in both younger and older Yakut men and women (P < 0.05). Lifestyle factors were significant predictors of BMR variation, particularly among older men and women.
  
  
  CONCLUSIONS
  Among the Yakut, increased wintertime BMR was observed among younger but not older adults, whereas all adults showed sharp reductions in free thyroid hormone levels during the winter. Among men, greater participation in subsistence activities was associated with increased BMRs and greater fat oxidation. Among women, variation in food use had the strongest impact on metabolic function.
authors.affiliation: Department of Anthropology, Northwestern University, Evanston, Illinois.
authors.forename: W R
authors.initials: WR
authors.lastname: Leonard
authors.forename: S B
authors.initials: SB
authors.lastname: Levy
authors.forename: L A
authors.initials: LA
authors.lastname: Tarskaia
authors.forename: T M
authors.initials: TM
authors.lastname: Klimova
authors.forename: V I
authors.initials: VI
authors.lastname: Fedorova
authors.forename: M E
authors.initials: ME
authors.lastname: Baltakhinova
authors.forename: V G
authors.initials: VG
authors.lastname: Krivoshapkin
authors.forename: J J
authors.initials: JJ
authors.lastname: Snodgrass
mesh_terms: D000328:Adult; D000368:Aged; D001110:Arctic Regions; D001481:Basal Metabolism; D058639:Cold-Shock Response; D005260:Female; D006801:Humans; D007124:Immunoenzyme Techniques; D008019:Life Style; D008297:Male; D008875:Middle Aged; D012621:Seasons; D012800:Siberia; D013974:Thyroxine / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood; D055815:Young Adult
chemical_list: D014284:Triiodothyronine; D013974:Thyroxine