We would like to thank Belfiore and Iannello (1) for their interesting questions regarding our study (2). We agree that lower insulin sensitivity in the San Antonio, Texas population could have contributed to the elevated incidence in this population compared with the Mexico City, Mexico population. Drs. Belfiore and Iannello calculated their insulin sensitivity index using the mean fasting and 2-h insulin values from our study because the raw data were not available to them. To address this question, we calculated the two indexes from the individual fasting and 2-h insulin values. Two indexes were calculated: ISI-a, a measure of insulin sensitivity based on the areas under the oral glucose tolerance test curve and ISI-b, a measure of insulin sensitivity in the basal state. As seen in Table 1, ISI-a was significantly higher in Mexico City, whereas ISI-b was not, thus confirming the calculations of Belfiore and Iannello. As noted by Belfiore and Iannello, these associations, which parallel the fasting and 2-h insulin values in Mexico City, could reflect impaired insulin secretion rather than enhanced insulin sensitivity.

Controlling for either ISI-a or -b did not attenuate the odds ratios reflecting the excess incidence of diabetes in San Antonio (Table 2). Thus, these indexes of insulin sensitivity do not account for the difference in incidence between the two cities. However, because these indexes may not be perfectly correlated with insulin sensitivity measured by a more definitive method, e.g., the euglycemic clamp, we do not dispute that differences in insulin sensitivity may account for part of the incidence difference between the two cities.

Table 1—

Age-adjusted baseline risk factors in Mexico City residents and San Antonio Mexican-Americans

Risk factorMen
Women
P for main effect of city
Mexico City (n = 578)San Antonio (n = 129)Mexico City (n = 801)San Antonio (n = 244)
ISI-a 1.25* 1.18 1.08* 1.03 0.0101 
ISI-b 1.15 1.15 1.10† 1.15 0.2954 
Risk factorMen
Women
P for main effect of city
Mexico City (n = 578)San Antonio (n = 129)Mexico City (n = 801)San Antonio (n = 244)
ISI-a 1.25* 1.18 1.08* 1.03 0.0101 
ISI-b 1.15 1.15 1.10† 1.15 0.2954 
*

P < 0.0001,

†

P < 0.01 for city comparisons within sexes; there were no significant city-sex interactions.

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Table 2—

Age-, sex-, and risk factor–adjusted odds of developing type 2 diabetes in San Antonio Mexican-Americans compared with Mexico City residentslegend

RRP95% CI
San Antonio versus Mexico City 1.84 <0.0001 1.36–2.46 
ISI(gly)-a Mexico City (0.50) 0.47 <0.0001 0.39–0.58 
    San Antonio versus Mexico City 1.86 <0.0001 1.37–2.51 
ISI(gly)-b (0.50) 0.50 <0.0001 0.41–0.61 
    San Antonio versus Mexico City 2.13 <0.0001 1.58–2.87 
RRP95% CI
San Antonio versus Mexico City 1.84 <0.0001 1.36–2.46 
ISI(gly)-a Mexico City (0.50) 0.47 <0.0001 0.39–0.58 
    San Antonio versus Mexico City 1.86 <0.0001 1.37–2.51 
ISI(gly)-b (0.50) 0.50 <0.0001 0.41–0.61 
    San Antonio versus Mexico City 2.13 <0.0001 1.58–2.87 
legend

There were no significant city–risk factor interactions.

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1
Belfiore F, Iannello S: Reduced insulin sensitivity in Mexican-Americans from San Antonio with elevated incidence of type 2 diabetes compared with Mexicans from Mexico City (Letter).
Diabetes Care
 
25
:
937
-938, 2002
2
Burke JP, Williams K, Haffner SM, Villalpando CG, Stern MP: Elevated incidence of type 2 diabetes in San Antonio, Texas, compared with that of Mexico City, Mexico.
Diabetes Care
 
24
:
1573
–1578,
2001

Address correspondence to James P. Burke, PhD, Department of Health Sciences Research, Harwick 6, Mayo Clinic, 200 First St. SW, Rochester, MN 55905. E-mail: [email protected].

2002