Artigos

Introduction
Colombia is a country with approximately 50 million inhabitants, where approximately 4.6 million people are older adults. Currently, life expectancy in Colombia is 77 years and in 2035 it will be approximately 80.4 years (1). In older adults the fat mass is redistributed throughout the body especially in the intra-abdominal or visceral area where an increase is noted. This increase is an important risk factor for various types of diseases such as cardiovascular disease, diabetes and risk of developing metabolic syndrome (2,3).
In Colombia, the criteria of the International Diabetes Federation (IDF) was adopted for the definition of metabolic syndrome. Its main criterion is abdominal obesity, which is linked to the other defining parameters (HDL cholesterol, triglycerides, fasting glucose and high blood pressure) (4,5).
The diagnosis of abdominal obesity is made by means of waist circumference measurement, which is an indicator of abdominal fat. This is not only a simple, low-cost and non-invasive anthropometric measurement, but it is also considered adequate for the diagnosis of this type of obesity (6). A high waist circumference is associated with elevated cardiometabolic risk markers irrespective of age, but there are differences in these associations in adults and older adults (7).
The Survey on Health, Well-Being, and Aging in Colombia (SABE Colombia study) evaluated the parameters for the definition of metabolic syndrome in older Colombian adults. Therefore, this study proposes to determine the waist circumference cut-off points of the Colombian older adult population specified by sex to define abdominal obesity and thus predict metabolic syndrome through the analysis of the SABE Colombia data. This, given the fact that there are no developed or validated cut-off points for the Colombian older adult population.

Methods
The SABE Colombia is a cross-sectional study, with sampling carried out using a stratified multistage probabilistic design for the population of non-institutionalized men and women aged 60 years or older. Additionally, SABE Colombia took into account the methods and procedures of the international SABE conducted by the Pan American Health Organization (PAHO) (8).
The final sample of SABE Colombia was 23,694 Colombian older adults, belonging to 244 municipalities in all departments of the country. However, the present study also took into account the sub-samples of the SABE study: measurement of blood pressure (n=5106), measurement of biochemical parameters (glycemia and lipid profile) (n= 4092) and measurement of waist circumference (n= 21,800). Thus, the sample of the present study was 3,812 persons who collected information to assess the risk markers of metabolic syndrome (HDL cholesterol, triglycerides, fasting glucose), blood pressure and anthropometric measurement of waist circumference.
Anthropometric measurements of weight, height and waist circumference were measured using a Seca - 803 digital scale, Seca 213 portable stadiometer and Seca precision tape measure, respectively. Blood pressure was measured using the OMRON HEM-705 sphygmomanometer. Waist circumference was measured in a standardized manner, with the patient facing the evaluator, standing upright with arms at the sides and back uncovered. An imaginary line was drawn from the axillary orifice to the iliac crest and the midpoint between the last costal arch (rib) and the upper part of the iliac crest (hip) was identified on this line (8).
Blood samples for the analysis of glycemia and lipid profile were taken from 2 out of every 5 persons surveyed and were taken at a clinical laboratory or, in case of difficulty in mobilization, these were done on an outpatient basis at the participant's place of residence; these samples were taken after the overnight fast and blood samples were collected in the morning hours. All samples were delivered to a single central laboratory (Dinámica laboratories, Bogotá Colombia) for analysis within 24 hours (8).
For the definition of metabolic syndrome, the IDF proposed abdominal obesity according to waist circumference as main criteria and in addition the presence of two or more of the following criteria: triglycerides > 150 mg/dl, HDL cholesterol <40 mg/dl for women and <50 mg/dl for men, blood pressure (systolic/diastolic) > 130/> 85 mmHg and blood glucose. > 100 mg/dl (9). However, for the classification of abdominal obesity there are different recommended values of waist circumference according to population and ethnic groups.
For the statistical analysis, the R software and the "OptimalCutpoints" and "pROC" packages were used. For the determination of the optimal cut-off point, an Operating Curve (ROC) analysis was performed, whose decision criterion was based on the maximization of the Youden Index calculated as J=Especificidad+Sensibilidad-1 (10) and multivariate logistic regression models were used to determine the odds ratios (OR) for predicting metabolic syndrome. Finally, the t-test was used to test averages and chi-square for the distribution of percentages, for which a significance level of 5% was defined.

Results
Of the 3,812 older adults studied, about 40% were men and 60% were women. Table 1 presents the age, anthropometric and the biochemical characterization of the studied population by sex. There was difference between all characteristics between men and women.
According to the area under the curve and the highest Youden Waist circumference index for predicting metabolic syndrome, the cut-off point was 91 cm for men and women with a sensitivity and specificity of 75% and 56% in men, respectively, and 68% and 53% in women (Figure 1). Table 2 shows the sensitivity, specificity, positive and negative predictive values of the waist circumference cut-off points for predicting metabolic syndrome in men and women, where it can be observed that the values proposed in our study present a better balance between sensitivity and specificity for the Colombian older adult population.
Table 3 shows how the parameters for the definition of metabolic syndrome behave according to the waist circumference cut-off point proposed for older adults (men and women). Significant differences were observed in HDL cholesterol, triglycerides, glucose and blood pressure in men and women with waist circumference less than 91 cm and greater than or equal to 91 cm, corroborating that this cut-off point has an impact on the other criteria used to define metabolic syndrome.

Discussion
The most adequate cut-off point for waist circumference for the definition of metabolic syndrome was 91 cm for both sexes in our study. The absence of waist circumference cut-off points supported by studies in the South American population is recognized (9,11). For older adults these studies are even scarcer. For this reason, in Colombia the cut-off points for waist circumference for the Asian population were adopted, which are >90 cm for men and >80 cm for women following the IDF recommendation (9). Additionally, the clinical use of cut-off points recommended by the National Cholesterol Education Program Adult Treatment Panel III (ATP III) for American adults of >102 cm for men and >88 cm for women is also common (12). However, there is evidence of inappropriate cardiovascular risk assessment based on the recommended cut-points for waist circumference in specific populations (13).
This is the first study that identified cut-off points for waist circumference in the older adult Colombian population for the definition of metabolic syndrome. The findings of our study suggest that it is not appropriate to use the cut-off points for the Asian population recommended by IDF, mainly for women, who presented a cut-off point 11 cm higher than this recommendation. Likewise, it is not appropriate to use the cut-off points recommended for the American population by ATP III, mainly for men, who presented a cut-off point 11 cm lower than this recommendation.
In our study, the cut-off point identified for older Colombian women is higher than those suggested for Asian and Caucasian women by IDF (80 cm) (9) and for American women by ATP III (88 cm) (12), being a little closer to the latter (higher by 3 cm). In a study carried out by Petermman-Rocha et al. (14) in the Chilean population, 87.6 cm was identified as the optimal waist circumference cut-off point for defining metabolic syndrome in women. A similar result was observed in the study by Cardinal et al. (15) with a waist circumference cut-off point of 86.6 cm in Brazilian women and Bermudez et al. (16) of 90.2 cm in Venezuelan women. Although those studies were conducted with South American population, neither was done specifically with older women, which is a possible explanation for the slightly higher optimal waist circumference cut-off point we found in our study for women. This, since older adult women tend to have a higher concentration of abdominal fat due to hormonal and body composition changes inherent to the aging process (2,3). In this aspect, using the cut-off points recommended by IDF or ATPIII to define metabolic syndrome in older Colombian women could overestimate the numbers of women in this age group who are really at risk.
The cut-off point derived for older Colombian men in our study is only 1 cm higher than that recommended for Asians (90 cm) and 3 cm lower than the cut-off point recommended for Caucasians (94 cm) by the IDF. In studies with similar approaches to ours, conducted with the Chilean, Brazilian and Venezuelan populations, 92.3 cm, 92 cm, 95.2 cm respectively were identified as optimal cut-off points for waist circumference in men (14-16). However, these studies were not specifically conducted with older adults.
In a study of 3,477 older adults in Brazil, it was observed that the cut-off points for waist circumference associated with overweight (body mass index greater than 27 kg/m2) was 91.5 cm for women and 97.5 cm for men (17). Nevertheless, it was not a cut-off point specifically identified for the definition of metabolic syndrome.
There is only one Latin-American study with older adults carried out in Ecuador, that determined 90.7 com for woman and 91.2 com for men as optimal waist circumference cutoff values for predicting metabolic syndrome (18). Our findings corroborate these results in elderly Latin Americans.
All reported South American cut-off points do not coincide with the IDF recommendations for women South Americans, but it was closer for men. Furthermore, there is no support in the literature for the use of Asian population reference values in the Colombian population. In fact, Asians correspond to less than 1% of the population living in Colombia (19).
The 91 cm waist circumference cutoff value can reduce the overestimate the numbers of women in this age group who are really at risk of metabolic syndrome. This could provide timely health care to those who really need to be prioritized, mainly, in Latin American countries that have limited health resources.
It can be concluded therefore that the calibration of waist circumference cut-off points for each population is of great relevance, since the prevalence of metabolic syndrome can be affected depending on the reference values of this anthropometric measurement used in its definition. Likewise, in addition to defining waist circumference cut-off points for different countries and ethnicities and according to sex, it is relevant to do so in different age groups, with adolescents and, as proposed in our study, in older adults.
Strength and limitations

This study was performed employing all the available data from SABE Colombia study, it has a large sample size designed with stratified randomized sampling methods, taking place in all geographical areas of Colombia. This study recruited the elderly from both urban and rural areas. In addition, all blood samples, systolic and diastolic blood pressure measures and anthropometric measures used to define metabolic syndrome were obtained by trained personal using standardized protocols (8).
Nevertheless, this study also has certain limitations. No institutionalized elderly participants were included; thus, some conclusions might not be directly applied to individuals living in long-term institutions or hospitalized older adults (8). Furthermore, given that this is a cross-sectional study without follow-up, this may not assist in determining causal associations between predicted determinants of health and outcomes. Future studies should corroborate this information investigating the association of these cut-off points with incidence and mortality for cardiovascular disease and all-cause mortality.

Acknowledgements
The SABE study is supported by a fund from Colciencias y Ministerio de Salud y la Protección Social de Colombia (2013, no. 764) and and by resources from Universidad Nacional de Colombia (Resolución 03/2017).
Disclosure statement
The authors declare no conflict of interest.

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