Ethnic differences in the association between waist-to-height ratio and albumin-creatinine ratio: the observational SUNSET study

BACKGROUND

Ethnic differences in the association between central obesity and raised albumin-creatinine ratio (ACR) have not been investigated. Our aim was to determine whether the association between central obesity, defined by the waist-to-height ratio (WHtR), and ACR differed between subjects of Hindustani-Surinamese, African-Surinamese and Dutch origin.

METHODS

In total, 334 Hindustani-Surinamese (~South Asian), 589 African-Surinamese (~African), and 493 Dutch (~European) men and women, aged 35-60 years, randomly selected from the municipal register of Amsterdam, participated in an interview and physical examination.We calculated the WHtR by dividing the waist circumference by height and the log ACR (logACR, log mg/mmol) by log-transforming the albumin concentration by the creatinine concentration in urine. The association between WHtR and logACR was studied in the total population and stratified by ethnicity. We also tested for interaction.

RESULTS

In the total population, a higher WHtR was associated with a higher logACR, after adjustment for sex, age, and smoking, body mass index and the presence of type 2 diabetes or hypertension. Among the Hindustani-Surinamese, the adjusted association between WHtR and logACR appeared somewhat stronger than among the other ethnic groups: for every 0.1 increase in the WHtR, the log-ACR increased by 0.522 (0.096-0.949) log mg/mmol among the Hindustani-Surinamese, by 0.334 (0.047-0.622) among the African-Surinamese and by 0.356 (-0.010-0.721) among the Dutch. However, the interaction was not statistically significant.

CONCLUSIONS

WHtR was associated with a higher ACR among populations of Hindustani-Surinamese, African-Surinamese and Dutch origin. Our study seems to support global use of WHtR in relation to ACR across ethnic groups. However, although not significant, the association appeared slightly stronger among the Hindustani-Surinamese than among the other ethnic groups. If confirmed, this could have implications for use of the WHtR across ethnic groups.

Lower frequency of the 5/5 homozygous CNDP1 genotype in South Asian Surinamese

We investigated the frequency of the 5/5 homozygous CNDP1 (carnosinase) genotype, which was found to be associated with a reduced risk of developing diabetic nephropathy, in three ethnic groups in The Netherlands. Particularly interesting were the South Asian Surinamese, who have a high prevalence of diabetic nephropathy. Furthermore, we investigated the association between this gene and carnosinase activity in South Asian Surinamese and whether carnosinase was expressed in the kidney. We genotyped 290 South Asian Surinamese, 532 African Surinamese, and 472 White Dutch in a cross-sectional population study. Furthermore, an independent cohort of South Asian Surinamese was genotyped. In this population, carnosinase activity was measured in serum. Immunostaining and in situ hybridization for CNDP1 were performed on kidney tissue. Both South Asian populations had lower frequencies of the 5/5 homozygous genotype than African Surinamese and White Dutch (23.0%, 27.2%, 38.2%, and 41.3%, respectively; chi-square, p<0.001). This genotype showed a lower carnosinase activity in South Asian Surinamese (Wilcoxon rank-sum, p=0.03). CNDP1 was expressed in the kidney. South Asian Surinamese have a lower frequency of the 5/5 homozygous genotype, which was associated with lower carnosinase activity. Our study provides an indication that South Asian Surinamese are genetically at risk for developing diabetic nephropathy.