Body Mass Index (BMI)

Transcription

1 Body Mass Index (BMI) Body mass index (BMI) is a simple, surrogate measure of body fatness. 1 BMI measures a person s excess body weight using a weight-to-height ratio. 2 Research has shown that BMI is highly correlated with body fat, however factors such as age, sex, ethnicity and muscle mass can influence the relationship between BMI and body fat. 1 In general, adults with a high BMI (overweight or obese) have a high percentage of body fat, and adults with a low BMI (underweight) have a low percentage of body fat. 1 The further away a person s BMI is from the normal range, the greater the risk of negative health effects (see Table 1). 1 Purpose of Health Indicator Report: To provide information about BMI for adults aged 18 and over in Halton Region Data Source: Rapid Risk Factor Surveillance System (RRFSS) 3 Data Collection Period: For more information on statistical significance, data interpretation and limitations in this report, see the data notes section on the last page. Table 1: Health Risk Classification According to Body Mass Index and Health Problems Associated with Body Weight 1 BMI Category (kg/m 2 ) Risk for Health Problems Problems Associated with Body Weight Underweight <18.5 Increased Under nutrition Osteoporosis Infertility Compromised immune function Normal Weight Least Overweight Increased Obese 30.0 High Type 2 diabetes Hypertension Coronary heart disease Gallbladder disease Obstructive sleep apnea Certain cancers Overall Findings: In 2013, 2% (±1)* of adults aged 18 and over in Halton Region were underweight, 43% (±3) were normal weight, 38% (±3) were overweight, and 17% (±2) were obese (see Figure 1). In 2011, adults aged 18 and over living in Halton were less likely to be obese [14%(±2)] than adults in Ontario [21%(±2]. This difference was statistically significant. There were no statistically significant differences between Halton and Ontario in the percent of adults who were underweight, normal weight and overweight. For the 2011 Ontario data and more information on the 2011 RRFSS provincial sample see the body mass index (BMI) provincial indicator report. 4

2 Trends Over Time: From 2001 to 2013 the percent of adults aged 18 and over in Halton who were normal weight decreased from 47% (±3) to 43% (±3), and this decrease was statistically significant (see Figure 1). From 2001 to 2013 the percent of adults aged 18 and over in Halton who were obese increased from 12% (±2) to 17% (±2), and this increase was statistically significant. From 2001 to 2013 there were no statistically significant changes in the percent of Halton adults aged 18 and over who were underweight or overweight (see Figure 1). Figure 1: Body mass index, adults aged 18 and over, Halton Region, Sex: In 2013, Halton females [53%(±4)] aged 18 and over were more likely than males [30%(±4)] to be normal weight (see Figure 2). This difference was statistically significant. In 2013, Halton males [49%(±5)] aged 18 and over were more likely than females [30%(±4)] to be overweight (see Figure 2). This difference was statistically significant. In 2013, there were no statistically significant differences by sex in the percent of adults aged 18 and over in Halton who were obese (see Figure 2). Figure 2: Body mass index, adults aged 18 and over, by sex, Halton Region, 2013

3 Age: In 2013, Halton adults aged were more likely than all other age groups to be normal weight (see Figure 3). This difference was statistically significant when comparing adults aged [64%(±13)] to adults aged [38%(±4)] and adults aged 65+ [39%(±5)] (see Figure 3). In 2013, older adults in Halton were more likely to be overweight than younger adults (see Figure 3). This difference was statistically significant when comparing adults aged [41%(±4)] to adults aged [20%(±11)]*, as well as when comparing adults aged 65+ [42%(±5)] to adults aged [20%(±11)]* (see Figure 3). In 2013, there were no statistically significant differences by age in the percent of Halton adults who were obese (see Figure 3). Figure 3: Body mass index, adults aged 18 and over, by age, Halton Region, 2013 Age Time Trend (Obesity): From 2001 to 2013, there was an overall increase in the percent of Halton adults who were obese (see Figure 1), however, this trend is primarily due to the increase in obesity in adults aged 45 to 64 from 13%(±4) to 20%(±4) (see Figure 4). From 2001 to 2013 there was no statistically significant difference in the percent of adults aged or aged 65 and over who were obese (see Figure 4). Figure 4: Percent of adults aged 18 and over who were obese, adults aged 18 and over, by age, Halton Region, 2013

4 Municipality: In 2013, there were no statistically significant differences by municipality in the percent of adults aged 18 and over in Halton who were normal weight, overweight or obese (see Figure 5). Figure 5: Body mass index, adults aged 18 and over, by municipality, Halton Region, 2013 Income: In 2013, obesity decreased as income increased, however this trend was not statistically significant (see Figure 6). In 2013, there were no statistically significant differences by income in the percent of adults aged 18 and over in Halton who were normal weight or overweight (see Figure 6). Figure 6: Body mass index, adults aged 18 and over, by income, Halton Region, 2013

5 Education: In 2013, there were no statistically significant differences by education in the percent of adults aged 18 and over in Halton who were normal weight, overweight or obese (see Figure 7). Figure 7: Body mass index, adults aged 18 and over, by education, Halton Region, 2013 Data notes on next page...

6 Data Notes: Definitions: BMI was calculated using self-reported height and weight (BMI=weight(kg)/height 2 (m)). Underweight refers to a BMI less than Normal weight refers to BMI between 18.5 and Overweight refers to a BMI between 25.0 and Obese refers to a BMI of 30.0 or greater. Statistical Significance: A 95% confidence interval (CI) refers to the range of values that has a 95% chance of including the true estimate. 95% CI s are reported in brackets or presented as I shaped bars in the graphs. A large CI means that there was a large amount of variability in responses or the sample size for the category was small. When CIs do not overlap between 2 or more groups (e.g., when comparing males and females) it means that the differences between the groups are statistically significant and unlikely to be due to chance alone. Since overlapping confidence intervals are used to determine statistical significance, p-values are not calculated. This is a conservative approach (α<0.01) which is more appropriate when multiple comparisons are being made, such as in this report. Trends over time were tested for significance using linear regression and autocorrelation. Data Interpretation: Income is based on the ratio of each survey respondent s annual household income level to the low income cut-off (LICO, 2011) corresponding to their household size, and community size. The low income group are those in the lowest 30% of income ratios, the middle income group are those in the 31st-70th% of income ratios and the high income group are those in the top 30% of income ratios. Respondents who did not know or refused to provide their income were excluded from the analysis. Coefficient of variation (CV) refers to the precision of the estimate. When the CV is between 16.6 and 33.3, the estimate should be interpreted with caution because of high variability and has been marked with an asterisk (*). Estimates with a CV of 33.3 or greater are not reportable and have been marked with double asterisks (**) in the graphs and tables. Household (HH) weights were used for any questions related to individuals. The HH weight adjusts for the fact that an adult in a larger HH is less likely to be selected than an adult in a smaller HH. Limitations: RRFSS results are self-reported and may not be recalled accurately. Individuals not living in households (such as those in prison, hospitals, or the homeless) were excluded. Individuals who live in a household without a landline telephone are also not reached through RRFSS (over 12% of all Ontario households, and 49% of Ontario households with only adults aged years old 5 ). As a result, the percentages may not represent the true estimates for the general population. Rounded estimates were used for the presentation of data, thus estimates may not total 100 percent. Rounded CI s were used for the presentation of data; however, non-rounded CI s were used to determine statistically significant differences. Don t know and refused responses were excluded from the analysis. Pregnant women and adults with a self reported height less than 0.91m or greater than 2.11m or with a self reported weight less than 35kg or greater than 260kg were excluded from analysis. References: 1. Centers for Disease Control and Prevention. (n.d.). Body Mass Index: Considerations for Practitioners. Retrieved June 5, 2014 from 2. Health Canada Canadian Guidelines for Body Weight Classification in Adults. Retrieved May 2014 from fn-an/nutrition/weights-poids/guide-ld-adult/index-eng.php 3. Rapid Risk Factor Surveillance System. ( 4. Rapid Risk Factor Surveillance System (RRFSS). Provincial Health Indicator Reports: Body Mass Index (BMI). Ontario, Canada: Rapid Risk Factor Surveillance System; 2011 [online]. Accessed May 23th 2014, from 20RRFSS%20Provincial%20Health%20Indicator%20Report.pdf 5. Statistics Canada Residential Telephone Service Survey (RTSS) (master file). Statistics Canada. Last Revised: June 17, 2014