[Analysis of vitamin A and thyroid blood levels in the indigenous and local Caucasian population of the Arctic].

Abstract

Previously, differences in the thyroid profile of Arctic residents were shown depending on the vitamin A blood level. However, dietary habits and metabolism peculiarities in the aboriginal and Caucasian representatives of the North population may be the cause of different retinol supply and therefore be one of the reasons for changes in their thyroid activity. The purpose of the research was to assess vitamin A and thyroid blood levels in the aboriginal and local Caucasian population representatives of the Russian Arctic territories. Material and methods. In the single-center observational cross-sectional study, apparently healthy residents of villages in the Arkhangelsk region were examined (n=281): 145 representatives of the local Caucasian population and 136 representatives of the aboriginal population, with the proportion of tundra nomadic aborigines at 34%, village aborigines at 66%. Vitamin A blood serum level was determined by the fluorometric method, and the thyroid content [thyroid stimulating hormone (TSH), thyroxine (T4), triiodothyronine (T3), free T4, free T3] was determined by enzyme immunoassay. The integral thyroid index (ITI) as well as the index of peripheral conversion of iodothyronine (IPC) total and free fractions were calculated. Results. The level of retinol in the indigenous population of the Arctic was lower than that in the local Caucasian population (1.84 [1.26; 2.56] versus 2.10 [1.70; 2.42] μmol/L, p=0.014). However, its deficiency was found only in village aborigines (20.5% of women and 11.8% of men). At the same time, they have the maximum tension of the pituitarythyroid system: lower level of free T3 and free fractions' IPC than in the nomadic and Caucasian population, and TSH levels were higher than in the Caucasian population. Increased vitamin A levels prevailed among the nomadic population: in 60.7% of men and 11% of women retinol level exceeded the norm. At the same time, they have increased metabolic activity of thyroid hormones: higher levels of free T3 and free fractions' IPC compared with sedentary aboriginal population. No pronounced features of the thyroid profile were found in local Caucasians at normal blood concentrations of vitamin A. Conclusion. The lowest retinol levels are observed in settled aborigines (especially young women) living in villages and experiencing the greatest transformation of traditional lifestyle and nutrition, which is combined with higher TSH blood levels and decreased thyroid hormone metabolism. The highest retinol levels were found in nomadic aborigines (especially young men), which increase the reserves of antioxidant defense and support high metabolism of thyroid hormones. However, the high percentage of people with excessive vitamin A blood level in this group raises concerns due to the possible negative consequences. Therefore, it is necessary to monitor fat soluble vitamin levels among Arctic aboriginal populations. Social support measures should be taken for settled residents of villages, enabling them to consume more traditional foods rich in vitamin A. The causes of excessive blood retinol in nomadic aborigines require further study and control.