Oda and Kawai (1) have reported that lower vital capacity (VC) (VC ≤96%) is associated with diabetes but not with the metabolic syndrome (MetS) in nonobese Japanese men and that no significant association between low VC, diabetes, and MetS was found in nonobese women. However, the coexistence of type 2 diabetes and MetS is often observed even in nonobese people (2,3). Furthermore, because both are mostly due to insulin resistance, we wondered whether their involvement in a specific pathology can also occur in normal-weight people.

Therefore, we reanalyzed the data from our ongoing cross-sectional study (4) to evaluate the associations between impaired pulmonary function and metabolic abnormalities in apparently healthy Japanese adults. We examined the relationship between low predicted forced VC (%PFVC) with MetS and diabetes in nonobese (BMI <25 kg/m2) Japanese men and women (n = 1,316 and 726, respectively). Exclusion criteria were the same as in the study by Oda and Kawai. MetS was defined according to the criteria of revised National Cholesterol Education (5) for Asians: waist circumference ≥90 cm for men and ≥80 cm for women. Diabetes was determined as already diagnosed by physicians or elevated fasting plasma glucose (≥126 mg/dl). Subjects were divided into quartiles according to %PFVC (men <86, 86–93, 94–100, and >100%; women <91, 91–97, 98–105, and >105%). Consequently, we found that compared with the highest %PFVC quartile (men n = 330, age 52.0 ± 11.3 years; women n = 186, age 53.8 ± 10.7 years), the lowest %PFVC quartile (men n = 327, age 52.3 ± 13.0 years; women n = 182, age 53.0 ± 13.2 years) was significantly associated with MetS in both men and women even after adjustment for age, smoking status, medications (hypertension and dyslipidemia), and waist circumference (odds ratio [95% CI]; men 1.93 [1.06–3.51], P = 0.03; women 4.90 [1.83–13.1], P = 0.002). By contrast, a significant association between lowest %PFVC quartile and diabetes was only observed in men (men 5.41 [2.03–14.4], P = 0.0007; women 1.35 [0.31–5.91], P = 0.69).

Taken together, low %PFVC may be associated with diabetes rather than MetS in nonobese men, which is partially consistent with the results of Oda and Kawai (1), and almost the opposite was observed in nonobese women. Furthermore, no significant difference in BMI and waist circumference was observed between nonobese subjects with lower %VC (≤96%) and those with higher %VC (men P = 0.56 and P = 0.58; women P = 0.12 and P = 0.41). The most plausible explanation for the inconsistency in results is that most of the subjects in their study would be lean with fewer cardiovascular risk factors because the overall prevalence of MetS was lower, even in nonobese subjects (men 4.7∼4.8%; women 2.2∼2.5%) compared with our subjects (men 9.4%; women 6.6%) with identical MetS criteria. Generally, people may have normal weight but occasionally exhibit metabolic abnormalities relating to insulin resistance (2,3). Thus, current findings suggest that low %VC, which commonly reflects restrictive lung, might also be associated with the characteristics of metabolically obese but normal weight (3).

No potential conflicts of interest relevant to this article were reported.

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