Lactose Malabsorption in Khants in Western Siberia M. LEMBER, A . TAMM, A. PIIRSOO, K. SUURMAA, K. KERMES, R. KERMES, T. SAHI & M. ISOKOSKI University of Tartu, Tartu, Estonia, and University of Helsinki, Helsinki, and University of Tampere, Tampere, Finland

Lember M, Tamm A , Piirsoo A , Suurmaa K, Kermes K, Kermes R, Sahi T, Isokoski M. Lactose malabsorption in Khants in Western Siberia. Scand J Gastroenterol 1995;30:225-227.

Background: We wanted to estimate the prevalence of selective lactose malabsorption (SLM) in Khants, a small Finno-Ugric population living in Western Siberia who have traditionally consumed no milk in adulthood. Merhods: A total of 80 Khants, aged 8-57 years and living on the middle reaches of the River Ob, were studied. The diagnosis was based on a lactose tolerance test; general malabsorption was excluded by a glucose-galactose tolerance test whenever possible. In six subjects electronmicroscopic examination of the duodenal mucosa was performed. Results: The prevalence of SLM in the Khants was 94%. Conclusion: This is the highest prevalence found in the previous Soviet Union.

Key words: Epidemiology; hypolactasia; lactose; lactose intolerance

Margus Lember, M.D., Dept. of Policlinic and Family Medicine, University of Tartu, Ulikooli 18, EE2400 Tartu, Estonia (fax: 372 7-428528)

The prevalence of genetically determined selective lactose malabsorption (SLM) and hypolactasia varies greatly between different nations and populations. In some peoples living in subarctic areas, like Eskimos and Indians in North America, the prevalence of SLM has been demonstrated to be high, exceeding 80% (1,2). In others, like Lapps in Europe, the prevalence is much lower; in different Lapp populations in the northernmost part of Finland, for example, the prevalence varies from 25% to 60% (3).

There are no data on SLM among other native northern peoples, most of them living in Siberia in Russia. In the food-help programs for these small-numbered peoples milk is often suggested even though their natural diet has not contained any milk in adulthood.

The purpose of this study was to estimate the prevalence of SLM, the main cause of milk intolerance, in one of the native peoples in Western Siberia, the Khants, who have traditionally consumed no milk in adulthood.

SUBJECTS AND METHODS

The Khants, whose total number is about 22,000, are a small ethnic group in Western Siberia, mostly on the middle reaches of the River Ob (Fig. 1). They are the easternmost branch of the Finno-Ugric language group. Their traditional way of life today still consists of hunting and fishing.

Most of the Khants live far away (up to 400-500 km) from the bigger villages; a few of them come to their central villages once a year for a limited number of days for shopping and their traditional ethnic festivals and to have their annual health check-up. All Khants who agreed to join the study when having the health check-up were examined for lactose malabsorption (LM).

The subjects of the study, a total of 80 people, were full- blooded Khants living in the Surgut region, about 650 km east of the Ural Mountains. There were 46 females and 34 males, and the mean age was 26 years (range, 8-57 years). The subjects belonged to either of two subgroups of the Khants: those who are mainly hunters (n = 30; center: the village of Russkinskije) and those who are mainly fishermen (n = 50; center: the village of Ugut).

The diagnosis of LM was based on a lactose tolerance test (50 g lactose was given in 400 ml water) performed after an overnight fast. The appearance of galactose in urine was determined 40 min after the lactose load, using a special test strip (Kabi Vitrum, Sweden). The criteria for LM were as described by Arola et al. (4) earlier. Besides the urine galactose determination, the blood glucose curve after the lactose load (0, 20, 40 min) was determined in 40 subjects. Blood glucose was measured with an Eyetone (Ames) color- imeter, using Dextrostix test strips and two parallel measure- ments. An increase in blood glucose level of less than 1.1 mmol/l was a criterion for LM (5).

To exclude the possibility of general malabsorption, all subjects with LM were asked to have a glucose-galactose tolerance test the next day (6). In six subjects a duodenal biopsy sample was taken to exclude suspected secondary malabsorption. The histologic structure of the duodenal mucosa was determined by electronmicroscopic examina- tion.

RESULTS

A total of 75 of 80 Khants (94%) fulfilled the criteria for LM. The prevalence was similar in males and females, in different age groups, and in hunters and fishermen. All

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Fig. 1 . Region in Western Siberia in Russia where the examined Khants live

children (n = 19) between the ages of 8 and 13 years were found to have LM.

Eighteen subjects with LM had a glucose-galactose tol- erance test. In 15 of them monosaccharides were absorbed normally, indicating SLM. In one person galactose was not found in urine, but the increase in blood glucose after the glucose-galactose load was high (2.9 mmol/l), which was indicative of SLM. In the other two subjects the glucose- galactose tolerance test result was abnormal, but the elec- tronmicroscopic examination of the duodenal mucosa did not show any major histologic changes in the brush border of the enterocytes. The reason for the abnormal glucose- galactose tolerance test result could not be found even though there were some slight changes in the cytoplasm of the epithelial cells. Probably, these two subjects also had SLM. No changes were shown by electronmicroscopic exam- ination in the duodenal mucosa of the other four subjects with duodenal biopsy sample. Their glucose-galactose tol- erance test results were also normal.

Thus, the prevalence of SLM and small-intestinal hypo- lactasia in the Khants was estimated to be 94%. If the two subjects who had abnormal glucose-galactose tolerance test results but no major changes in their duodenal mucosa had non-selective (and non-genetic) LM, we can estimate that at least 89% (16 of 18) of those with lactose malabsorption had SLM. On the basis of this, a prevalence of 83% can be calculated as a lower point estimate of the prevalence of SLM.

DISCUSSION

The present study shows that the Khants belong to the group of populations with a very high prevalence of SLM, like most of the other peoples living in far northern areas. The result was as expected in advance. Because milk has never been a part of the traditional diet of the Khants, the high

prevalence can be explained by the culture-historical hypoth- esis (7). according to which the prevalence of SLM is nega- tively correlated with the duration of milk consumption by the population.

The age of onset of SLM in Khants is low, less than 8 years of age, because all children from the age of 8 to 13 had LM. This result is consistent with the previous finding that, in general, peoples with high prevalence of SLM have a low age of onset (8).

There were possibly a few subjects who had secondary lactose malabsorption, although no major histologic changes could be found in small-intestinal biopsy samples from six subjects with LM. It is possible that opistorchosis, which is widespread among Khants, could reduce the absorption of di- and mono-saccharides without major histologic changes in the mucosa of the small intestine (9). No opistorchosis was, however, diagnosed.

The prevalence of SLM (94%) among the Khants is the highest prevalence found in the populations of the previous Soviet Union. It is significantly higher than the prevalence of 81% among the Mari people (lo), another branch of the Finno-Ugric language group, living on the middle reaches of the Volga River. The Maris are the easternmost popu- lation in Europe whose SLM prevalence has been deter- mined.

The prevalence of SLM in the Khants is also significantly higher than that among Russians (57%) from the western part of Russia (11). The high prevalence of SLM in the Khants is consistent with the gradual west to east increase in SLM prevalence observed in central and eastern Europe (11,12).

ACKNOWLEDGEMENTS

The authors express their gratitude to Olympus Co. for providing endoscopes for the field studies in Western Siberia,

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Lactose Malabsorption in Khanrs 227

to the authorities of t he Surgut Region for support in per- forming the examinations, and to Dr. G. Suurvali for his kind support in preparing the expedition.

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6. Sahi T, Isokoski M, Jussila J, Launiala K. Lactose malabsorption in Finnish children of school age. Acta Paediatr Scand 1972;61: 11-6.

7. Simoons FJ. Primary adult lactose intolerance and the milking habit: a problem in biological and cultural interrelations. 11. A culture historical hypothesis. Am J Dig Dis 1970;15:695-710.

8. Simoons FJ. Age of onset of lactose malabsorption. Pediatrics 1980;66:6468.

9. Yablokov DD. Opistorchosis in men. Tomsk, 1979 (in Russian). 10. Tamm A, Lember M, Siigur U, Vija M, Arola H, Sahi T, et

al. Prevalence of lactose malabsorption (LM) in adult Mari population (abstract). In: Klaukka T, Piha T, Poikolainen K, Sahi T, editors. International Epidemiological Association XI Scientific Meeting. Abstracts. Helsinki: IEA, 1987:153.

11. Lember M, Tamm A, Villako K. Lactose malabsorption in Estonians and Russians. Eur J Gastroenterol Hepatol 1991 ;3: 479-81.

12. Sahi T. Genetics and epidemiology of adult-type hypolactasia. Scand J Gastroenterol 1994;29 Suppl 202:7-20.

Received 1 February 1994 Accepted 22 June 1994

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