Elevated resting metabolic rates among female, but not male, reindeer herders from subarctic Finland

Abstract

Objective: Elevated resting metabolic rates (RMR, kcal/day) are a wellestablished mechanism for maintaining core body temperature among cold climate populations. A high degree of interindividual variation has recently been noted among circumpolar populations. To further examine RMR variability, we investigated anthropometric and metabolic differences among reindeer herders from subarctic Finland. Methods: Resting metabolic rates, body mass, body composition, height, age, and sex were measured among 20 reindeer herders (5 females, 15 males, 20-64 years) from seven herding districts surrounding the Arctic Circle of Finland in January of 2019. Results: Females had a mean RMR of 1798 ± 216 kcal/day and males 1753 ± 503 kcal/day. When controlling for body mass and fat-free mass, females had significantly higher RMRs relative to males (P < .01). Contrary to previous cold climate population studies, measured RMR among males was not significantly different from predictive equation estimates (P > .05). However, predictive equations significantly underestimated female RMR by a mean of 25.2% ± 5.9% (P < .01). Conclusion: These results mirror earlier findings, though in ways previously unseen. In this population: (a) There is a high degree of RMR interindividual variability, but only among males, and (b) there is evidence for elevated RMR, but only among females. Though the sample size is small, preliminary results suggest the presence of sex-based differences in metabolic adaptations to cold climates within this population subset. Potential reasons for this sex-based difference are discussed including a presentation of a hypothesis about the dual role of thyroid hormone in both reproductive and metabolic processes.

No association of BMI and body adiposity with cardiometabolic biomarkers among a small sample of reindeer herders of sub-Arctic Finland

“…Although there was a large age range (20–64 years) among participants in this study, it is possible with a small sample size that we were unable to detect the impact of age on the emergence of a poor cardiometabolic profile. This could explain why no females were categorised as obese in this sample, as could the higher resting metabolic rate documented among females in this sample previously [ 38 ]. However, female representation in this study is poor, and a greater number of female participants would provide a better indicator if there are true sex differences in the prevalence of obesity.…”

“…This study is part of a larger project, “The metabolic cost of living among reindeer herders in northern Finland, 2017–2020” assessing the biological and cultural mechanisms for coping with a highly demanding occupation in an extreme cold environment. This larger project incorporated measurements of resting metabolic rate [ 38 ], brown adipose tissue activity [ 39 ], total energy expenditure [ 36 ], and ethnographic interviews [ 37 ]. Reindeer herders in Finland are both Indigenous Sami and Finnish, and their herding work blends traditional and modern technologies and practices [ 37 ].…”

“…During the winter, herders are occupied with daily reindeer feeding in the winter enclosures, bookkeeping, and sometimes tourism [ 37 ]. We have provided a more detailed description of reindeer herding and of the herders elsewhere [ 37 , 38 ].…”

“…Four-site skinfold thicknesses were also collected and measured. However, there was no significant difference between the bioelectric impedance values and skinfold measures [ 38 ]. Only bioelectrical impedance results were used for further analysis.…”

“…Furthermore, Finland has some of the highest rates of cardiovascular disease in the world, though this is declining [ 33–35 ]. However, less is known about reindeer herders in Finland who are highly physically active due to participation in subsistence practices [ 36 , 37 ], and exhibit an unusual metabolic pattern with females having higher resting metabolic rates than males [ 38 ]. Here we examine the relationship between BMI, body adiposity, and cardiometabolic health biomarkers (fasting glucose, total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein, and triglyceride levels) among a small sample of highly active cold climate population of reindeer herders from sub-Arctic Finland.…”