The present cross-sectional study results showed that VFA ≥ 125 cm2 was significantly positively associated with DM compared to VFA ≥ 65 cm2 in men, and VFA ≥ 85 cm2 was significantly positively associated with DM compared to ≥ 30 cm2 in women after adjusting for confounders. SFA ≥ 135 cm2 was significantly positively associated with DM compared to SFA ≥ 90 cm2 in women, whereas no association was observed in men. VFA was closely and positively associated with DM in both sexes, and appropriate estimated cut-off points might be 101.5 cm2 in men and 72.5 cm2 in women for DM, respectively. SFA was also associated with DM only in women, suggesting a cut-off value of 165.3 cm2. To the best of our knowledge, analyses of the association between DM and VFA and SFA are limited.
Visceral fat accumulation is widely regarded as a risk factor for cardiovascular diseases, including DM. Mets is a metabolic condition that predicts individuals who are likely to be affected by cardiovascular disorders via insulin resistance . One major feature of Mets is visceral fat accumulation, which is closely related to insulin resistance. Visceral fat accumulation is generally recognized as a WC > 85 cm2 in men and > 90 cm2 in women, which correspond to a VFA of 100 cm2 in an abdominal CT scan at the umbilical level . Visceral fat accumulation is also known to be an independent risk factor for type 2 diabetes. A longitudinal study that determined the optimal cut-off value of VFA for predicting type 2 diabetes among 13,004 Koreans reported values of 118.8 cm2 in men and 82.6 cm2 in women . Another longitudinal survey that followed Japanese Americans for 10 years reported a baseline intra-abdominal fat area (IFA) of 102.7 cm2 in the incident diabetes group and 74.3 cm2 in those without incident diabetes, respectively. Also, an increase of 1 SD in IFA was associated with a 1.65-fold increase in the odds of diabetes over 10 years (OR = 1.65, 95% CI = 1.21–2.25) after adjusting for the above covariates . These previous study results are closely similar to our results. Thus, sex-specific reference values for visceral fat accumulation such as that men with a VFA ≥ 100 cm2 and women with a VFA ≥ 80 cm2 should be considered to prevent and manage type 2 diabetes.
Our results showed that SFA was significantly positively associated with DM in women, whereas no association was observed in men. The role of subcutaneous fat in cardiovascular risk remains controversial. The Shanghai Nicheng Cohort Study, which was conducted among 12,137 Chinese adults aged 45–70 years, reported multivariable-adjusted ORs and 95% CIs of newly diagnosed diabetes per 1-standard deviation increase in SFA and VFA of 1.29 (1.19–1.39) and 1.61 (1.49–1.74) in men and 1.10 (1.03–1.18) and 1.56 (1.45–1.67) in women, respectively . However, the association between SFA and newly diagnosed diabetes disappeared in men and was reversed in women (OR 0.86 [95% CI, 0.78–0.94]) after additional adjustment for BMI and VFA . A study that surveyed 3,001 participants from the Framingham Heart Study reported that multivariable-adjusted general linear regression analyses of SAT and VAT showed significant associations with blood glucose in both sexes [age-adjusted Pearson correlation coefficients; 0.23 for SAT and 0.34 for VAT in women (P < 0.001), 0.12 for SAT and 0.19 for VAT in men (P < 0.001)]. In addition, the magnitude of association between VAT and all risk factors was greater for women than men, and weaker sex differences were observed for SAT . The Jackson Heart Study, which surveyed 2,477 African Americans, reported that abdominal VAT and SAT were both associated with adverse cardiometabolic risk factors, including diabetes, and the effect size of VAT in women was larger than that of SAT [fasting plasma glucose, 5.51 ± 1.0 vs. 3.36 ± 0.9; diabetes, 1.82 (1.6–2.1) vs. 1.58 (1.4–1.8); and Mets, 3.34 (2.8-4.0) vs. 2.06 (1.8–2.4), respectively; P < 0.0001 for difference between VAT and SAT] . The possible mechanism of the association between diabetes and SAT as well as VAT is insulin resistance. To date, numerous studies have assessed the association between excess visceral fat accumulation and insulin resistance. Regarding SAT, several previous surveys indicated a positive association between excess subcutaneous fat accumulation and insulin resistance. A Japanese study that surveyed 912 non-diabetic participants reported that subjects in higher tertiles of SAT and VAT had significantly higher HOMA-IR and lower Matsuda ISI levels (P < 0.001) . Excess SAT accumulation may cause insulin resistance and contribute to glucose intolerance as well as VAT. Therefore, it is necessary to consider adiposity, including SAT and VAT, to better maintain body composition.
In regard to the impact of SAT, a sex difference was observed. There is little evidence available to explain the difference. The Jackson Heart Study, which involved 2,799 African Americans, reported a direct association between SAT and adiponectin (β = 0.18; P = 0.002) that persisted when controlling for BMI and WC among men, whereas the significance was borderline among women (β = 0.05; P = 0.05) . Although the evidence is limited to explain the sex difference, it is possible that adiponectin may contribute. Further analyses are required to assess the sex difference.
Our study has several limitations. First, it was susceptible to selection bias, as the participants consisted of those who received voluntary medical check-ups at a single medical institution. As such, these participants may be inherently more aware of their health behaviors relative to the general population. Second, this was a cross-sectional observational study, thus limiting consideration of the causal relationship between SFA/VFA and DM. Further analyses that include data from a more diverse cohort are thus needed. Third, some key data regarding items such as details of diabetes medications, eating behaviors, and nutritional status were not collected. Future prospective studies including these data are also needed.
In conclusion, the results of the present cross-sectional study indicate that VFA ≥ 125 cm2 in men is significantly positively associated with DM compared to VFA ≥ 65 cm2, and VFA ≥ 85 cm2 in women is significantly positively associated with DM compared to VFA ≥ 30 cm2 after adjusting for confounders. SFA ≥ 135 cm2 in women is significantly positively associated with DM compared to SFA ≥ 90 cm2, but no association was observed in men. Appropriate estimated VFA cut-off points for DM are 101.5 cm2 in men and 72.5 cm2 in women, respectively. As SFA was associated with DM only in women, the appropriate estimated cut-off is 165.3 cm2. Our results suggest that it is important to consider both SFA and VFA, especially in women, for primary and secondary prevention of DM.