This study explored the associations between fitness and fatness with the presence of metabolic syndrome in an understudied population of midlife and older rural US Midwestern women with prehypertension. Because the cohort consisted of women with documented prehypertension, we anticipated these women might have a high prevalence of metabolic syndrome. Though rural populations differ from each other, our findings that 31% of this cohort had metabolic syndrome was similar to the work of Vaughan and associates [15
] who reported that 33% of rural Australian women ages 25–74 years were classified as having metabolic syndrome. However, our prevalence of metabolic syndrome (31%) was much less than the 40.2% reported for rural women across the USA from the 1999–2006 NHANES data [5
], perhaps in part due to our inclusion/exclusion criteria which included women able to walk one-mile without assistance and excluded women with hypertension.
While the overall cohort had a high percentage (40.1%) who reported their quality of health being very poor to fair, the percentage of women with metabolic syndrome who rated their health as very poor to fair was much higher (51%). This is consistent with findings from other rural US Midwestern women [12
]. Of those with metabolic syndrome, the finding of a high prevalence of both obesity and low estimated cardiorespiratory fitness are of concern, as the evidence demonstrates that obesity, particularly abdominal obesity, is a core component of metabolic syndrome [7
] and that a minimal level of cardiorespiratory fitness is important for overall health [45
Our results are consistent with the work of Shah and Braverman [27
] who compared BMI to a direct determination of percent body fat using duel energy X-ray absorptiometry (DXA) with findings that NIH-based BMI standards for defining obesity significantly underestimated the prevalence of obesity, especially in women with advancing age. Although we used the bioelectrical impedance method for estimating percent body fat which has a large standard of error estimation of 3.5 to 5.0% and tends to underestimate the percent body fat compared to the gold standard of dual-X-ray absorptiometry (DXA), we felt that examining body composition using bioelectrical impedance analysis for percent body fat would further inform this study of rural women [37
]. We did attempt to reduce the risk of measurement error by having the participants follow pre-test control conditions that affect hydration levels.
As noted by Shah and Braverman [27
], BMI may ignore the influence of sarcopenic obesity in aging women. For this reason, several groups of researchers have attempted to identify new cut-points for BMI that would better categorize individuals as obese, with studies suggesting obesity cut points for women should range from 24 to 25.5
]. Our results also suggested the NIH BMI cut-score (≥30
) for obesity misclassified 50.5% of women who were defined as obese by percent body fat; however, the revised BMI cut-score resulted in a more similar percentage of women classified as obese (81.6%; n
= 236) as those classified obese by body fat (94.5%; n
= 273). Using a revised cut-score of ≥25
to better categorize women as “fat” may explain why we found that “fit/fat” women (see ) had lower odds of prevalent metabolic syndrome similar to that when using percent body fat in the analysis. Rural practitioners may want to consider using this revised BMI score to define obesity in midlife and older women.
While obesity is highly associated with a cluster of metabolic abnormalities, current studies suggest that 20–30% of obese individuals appear to maintain a favorable metabolic profile [8
], perhaps due to having a higher cardiorespiratory fitness level. Aging has been associated with a decrease in lean mass and an increase in percent body fat, both which have been identified as contributing to the development of metabolic syndrome [7
]. Hassinen et al. [23
] studied women ages 57–79 with results that indicated low cardiorespiratory fitness could be considered a feature of metabolic syndrome. They used a more accurate measure of fitness, symptom-limited maximal exercise stress test on a cycle ergometer, in contrast to our 1-mile walk test which provided an estimate of cardiorespiratory fitness. Our findings were similar to Hassinen and colleagues [23
] in that when examining the association of fitness alone with the presence of metabolic syndrome, women with higher fitness had 7% lower odds of having metabolic syndrome and fitness was associated with lower odds of metabolic syndrome when classified as “fit/fat” by either the percent body fat cut-score or the revised BMI cut-score. When we entered both % body fat and fitness as continuous variables, fitness was not significant. Our finding is also similar to Hassinen and associates [23
] who found that abdominal obesity as measured by waist circumference markedly weakened the association between cardiorespiratory fitness and metabolic syndrome.
Our study is unique in that it included successful recruitment of a large sample of midlife and older rural women with prehypertension, an understudied population that is recognized for having health disparities. This study included complete data for all variables and included two body composition measures (percent body fat in addition to BMI) and an objective measure of estimated cardiorespiratory fitness.
Several limitations are noted. The cross-sectional design limited any interpretation of causality. Because recruitment used a convenience sample of female volunteers, the women in this study may not have been representative of, or generalizable to, the overall population of women of that region. There was potential for misclassification of both “fitness” and “fatness” due to the limitations of measurement methods selected for use in this community-based clinical trial (percent body fat via bioelectrical impedance and fitness via the 1-mile submaximal field test) as opposed to more direct, complex laboratory studies of DXA for percent body fat and a maximal, graded exercise test for fitness. Our women may not have been representative of the population-at-large as they were not hypertensive, able to walk at least one mile unassisted, and were volunteers seeking a lifestyle intervention to reduce blood pressure. In addition, we did not examine medications that might impact weight nor did we collect the proportion of women on statins or other lipid-lowering agents.
In conclusion, these rural women with prehypertension had a high prevalence of metabolic syndrome, placing them at high risk for cardiovascular disease. Metabolic syndrome was associated with a high prevalence of obesity, lower estimated cardiorespiratory fitness, and more self-reports of poor to fair health status. NIH BMI-based classifications appeared to underestimate obesity in this population whereas the revised BMI cut-score produced results that were similar to the percent fat cut-scores for defining obesity. Rural practitioners may find using a BMI cut-score of ≥25
to be useful in defining obesity in this population.
Obesity and fitness, each alone, was associated with metabolic syndrome. There is an indication that fitness may be important to reducing the risk of metabolic syndrome, though the presence, and potentially the degree of fatness, may reduce this association.