Relationship of the American Heart Association's Impact Goals (Life's Simple 7) With Risk of Chronic Kidney Disease: Results From the Atherosclerosis Risk in Communities (ARIC) Cohort Study
Background As part of its 2020 Impact Goals, the American Heart Association developed the Life's Simple 7 metric for cardiovascular health promotion. The relationship between the Life's Simple 7 metric and incident chronic kidney disease (CKD) is unknown.
Methods and Results We estimated the association between Life's Simple 7 and incident CKD in 14 832 Atherosclerosis Risk in Communities study participants. Ideal levels of Life's Simple 7 health factors were the following: nonsmoker or quit >1 year ago; body mass index <25 kg/m2; ≥150 minutes/week of physical activity; healthy dietary pattern (high in fruits and vegetables, fish, and fiber‐rich whole grains; low in sodium and sugar‐sweetened beverages); total cholesterol <200 mg/dL; blood pressure <120/80 mm Hg; and fasting blood glucose <100 mg/dL. At baseline, mean age was 54 years, 55% were women, and 26% were African American. There were 2743 incident CKD cases over a median follow‐up of 22 years. Smoking, body mass index, physical activity, blood pressure, and blood glucose were associated with CKD risk (all P<0.01), but diet and blood cholesterol were not. CKD risk was inversely related to the number of ideal health factors (P‐trend<0.001). A model containing the Life's Simple 7 health factors was more predictive of CKD risk than the base model including only age, sex, race, and estimated glomerular filtration rate (Life's Simple 7 health factors area under the ROC curve: 0.73, 95% CI: 0.72, 0.74 versus base model area under the ROC curve: 0.68, 95% CI: 0.67, 0.69; P<0.001).
Conclusions The AHA's Life's Simple 7 metric, developed to measure and promote cardiovascular health, predicts a lower risk of CKD.
The 2020 Impact Goals of the American Heart Association (AHA) are to achieve a 20% improvement in cardiovascular health and 20% reduction in deaths due to cardiovascular disease and stroke in the United States by the year 2020.1 To achieve these goals, the AHA recommended 7 healthy factors for cardiovascular disease prevention—Life's Simple 7—related to total cholesterol, fasting blood glucose, blood pressure, smoking, body mass index, physical activity, and diet.2 The diet recommendation addresses 5 components (fruits and vegetables, fish, fiber‐rich whole grains, sodium, sugar‐sweetened beverages) selected, in part, for consistency with the US Dietary Guidelines for Americans and AHA scientific statements.3, 4, 5
Aside from cardiovascular disease, several studies have reported on the relationship between AHA Life's Simple 7 and risk of other outcomes such as diabetes,6 depression,7 stroke,8 and cognitive impairment.9 The shared underlying pathophysiology leading to the development of cardiovascular and kidney disease suggests that cardioprotective recommendations might also be effective for kidney disease prevention.10 Two studies have investigated Life's Simple 7 and kidney disease progression among individuals with impaired kidney function.11, 12 However, to the best of our knowledge, it is not known whether this combination of health factors as defined by AHA Life's Simple 7 is associated with incident chronic kidney disease in a general population. Determining the relationship between AHA's Life's Simple 7 and chronic kidney disease could not only illustrate the potential influence of the 2020 Impact Goals on kidney disease in the general population but also inform the design of public health interventions for kidney disease prevention.
Our objective was to assess the relationship of the overall Life's Simple 7 metric, the individual health factors, and each diet component with risk of incident chronic kidney disease in a large, community‐based cohort free of chronic kidney disease at baseline.
Study Design and Population
The Atherosclerosis Risk in Communities (ARIC) study is a community‐based cohort of 15 792 middle‐aged (45–64 years of age), predominantly black and white men and women.13 Study participants were recruited and enrolled in 1987–1989 from 4 US communities: Forsyth County, North Carolina; Jackson, Mississippi; suburbs of Minneapolis, Minnesota; and Washington County, Maryland. Follow‐up study visits occurred in 1990–1992 (visit 2), 1993–1995 (visit 3), 1996–1998 (visit 4), and 2011–2013 (visit 5). An ethics committee at each site approved the study protocol, and study participants provided informed consent at each study visit. After excluding participants with chronic kidney disease (defined using the same criteria as the chronic kidney disease outcome as described below) at baseline (n=356) and participants with missing data for any of the 7 health factors (n=604), the sample size was 14 832 (Figure 1). The current study is a prospective analysis of the ARIC study to characterize the relationship of Life's Simple 7 factors assessed at baseline (1987–1989) and the development of incident kidney disease during follow‐up through the end of 2010. Aside from having the event (incident chronic kidney disease), study participants were censored due to death from a cause other than kidney disease, loss to follow‐up, or the end of the observation period.
At baseline, trained interviewers administered a questionnaire to collect information on demographic characteristics, health behaviors, medical history, and medication use. Body mass index was calculated as weight (in kilograms) divided by height (in meters squared) using measurements taken during the baseline study visit. After 5 minutes of rest, 3 seated measurements of blood pressure were taken by a certified technician using a random‐zero sphygmomanometer. The mean of the second and third blood pressure measurements was used for analysis.
Fasting blood samples were collected during study visits. Blood levels of glucose were measured by the modified hexokinase/glucose‐6‐phosphate dehydrogenase method. Blood levels of creatinine were measured by the modified kinetic Jaffe method, calibrated to account for differences in laboratory tests, and standardized to the National Institute of Standards and Technology standard.14, 15 Total blood cholesterol concentration was assessed by enzymatic procedures.16
Usual dietary intake was assessed at baseline using a semiquantitative 66‐item food‐frequency questionnaire administered by trained interviewers to improve accuracy and completeness.17, 18 Frequency and portion size of each food item was multiplied by nutritional content from US Department of Agriculture sources to estimate intake of micro‐ and macronutrients.
Categorization of Life's Simple 7 Health Factors
Individual health factors were categorized as poor, intermediate, or ideal according to the AHA Life's Simple 7 criteria (Table 1). Ideal levels of health factors were: nonsmoker or quit >1 year ago; body mass index <25 kg/m2; ≥150 minutes/week of physical activity; healthy diet score (see below); total cholesterol <200 mg/dL; blood pressure <120/80 mm Hg; and fasting blood glucose <100 mg/dL. Study participants who were treated to target levels for hypercholesterolemia, hypertension, or diabetes were classified as intermediate for the respective health factor.
The healthy diet score was calculated as the sum of the scores for each of 5 individual components for which the recommended intake levels were: (1) ≥4.5 servings of fruits and vegetables per day; (2) ≥7 ounces of fish per week; (3) ≥3 ounces of fiber‐rich whole grains per day (≥1.1 g of dietary fiber/10 g of carbohydrate per day); (4) <1500 mg of sodium per day; and (5) ≤36 ounces of sugar‐sweetened beverages per week (Table 2). The range is from 0 to 5, with a lower score being unhealthy.
Measurement of Other Covariates
Diabetes was defined at baseline as fasting blood glucose ≥126 mg/dL, non‐fasting glucose ≥200 mg/dL, reported history of diabetes, or use of diabetes medication in the preceding 2 weeks. Hypertension was defined as systolic blood pressure ≥140 mm Hg, diastolic blood pressure ≥90 mm Hg, or use of antihypertensive medication in the preceding 2 weeks. Estimated glomerular filtration rate (eGFR) was calculated with standardized serum creatinine according to the Chronic Kidney Disease Epidemiology Collaboration (CKD‐EPI) estimating equation.19
Ascertainment of Chronic Kidney Disease Cases
Incident chronic kidney disease was assessed from baseline through December 31, 2010 and defined as (1) development of eGFR <60 mL/min per 1.73 m2 accompanied by ≥25% eGFR decline, (2) International Classification of Diseases 9/10 code for a hospitalization due to chronic kidney disease identified by surveillance of hospitalizations and annual follow‐up phone calls with study participants, (3) International Classification of Diseases 9/10 code for a death due to chronic kidney disease identified by linkage to the National Death Index, or (4) end‐stage renal disease identified by linkage to the US Renal Data System registry.20 As a sensitivity analysis, incident chronic kidney disease was defined using visit‐based measures (ie, eGFR <60 mL/min per 1.73 m2 at a subsequent study visit accompanied by ≥25% eGFR decline relative to baseline).
Descriptive statistics (mean, SD, proportion) were used to describe baseline characteristics according to the number of ideal Life's Simple 7 factors. Differences in baseline characteristics by number of ideal health factors were evaluated using tests for trend.21
We used Cox proportional hazards regression to estimate chronic kidney disease risk according to categories of the 7 individual health factors (ideal, intermediate, poor) in the same model, the overall metric (number of ideal health factors), and categories of the 5 individual diet characteristics. The categories for 6 and 7 ideal health factors were collapsed together due to the small number of participants and absence of chronic kidney disease events among these participants with all 7 ideal health factors. Multivariable regression models were adjusted for demographic characteristics (age, sex, and race) and baseline kidney function (eGFR modeled as 2 linear spline terms with a knot at 90 mL/min per 1.73 m2). For the individual components of the healthy diet, we additionally adjusted for body mass index, physical activity, diabetes, and hypertension. We tested for trend in risk estimates according to ordered categories (ideal, intermediate, poor) for the 7 individual health factors, number of ideal health factors, and levels of dietary intake of the 5 diet factors as continuous variables. Harrell's C statistic was used to calculate area under the receiver operating characteristic curve (AUC). Linear combinations were used to test for differences between AUC values for the base model including age, sex, race, and eGFR versus the expanded model including all of the Life's Simple 7 factors plus the base model. Sensitivity analyses were conducted to assess different definitions of the healthy diet score. Effect modification by race and sex was assessed by stratified analysis and tests of interaction. Analyses were conducted using Stata statistical software version 13 (StataCorp LC, College Station, TX).
In the overall study population, mean age at baseline was 54 years, 55% were women, and 26% were African American. Younger age, female sex, and white ethnicity were associated with a higher number of ideal levels of Life's Simple 7 health factors (P<0.001 for all; Table 3). Body mass index, systolic blood pressure, and proportion of people with diabetes and hypertension—all health characteristics incorporated into the Life's Simple 7 metric—were lower with higher Life's Simple 7 scores (all P<0.001). Kidney function also varied according to number of ideal Life's Simple 7 health factors, but the absolute differences in eGFR values were small. There was no significant trend in total caloric intake according to number of ideal health factors.
Distribution of Ideal Health Factors
The largest proportion of the study population meeting ideal criteria was for cigarette smoking (72.4%; Table 4). Having an ideal healthy dietary pattern was the rarest (6.2%). Over half of the study population had 2 or 3 ideal health factors (Table 5). A small proportion of the population met none of the ideal criteria (2.6%) and a similar number of study participants met the ideal criteria for 6 or 7 health factors (2.8%).
Individual Health Factors and Risk of Incident Chronic Kidney Disease
Over a median follow‐up of 22 years (271 285 total person‐years), there were 2743 incident chronic kidney disease cases. Compared to poor levels of health factors, the risk of chronic kidney disease was lower with intermediate and ideal levels of health factors for smoking, body mass index, physical activity, blood pressure, and fasting blood glucose (all P for trend <0.01; Table 4). The strongest association with chronic kidney disease risk was observed with ideals levels of fasting blood glucose (hazard ratio [HR] for ideal: 0.37, 95% CI: 0.33, 0.41; HR for intermediate: 0.40, 95% CI: 0.36, 0.45) followed by blood pressure (HR for ideal: 0.50, 95% CI: 0.44, 0.56; HR for intermediate: 0.73, 95% CI: 0.67, 0.81). Ideal levels of the healthy diet score (P‐value for trend=0.55) and total cholesterol level (P‐value for trend=0.62) were not associated with incident chronic kidney disease.
A model containing the Life's Simple 7 health factors was more predictive of chronic kidney disease risk than the base model including only age, sex, race, and eGFR (ideal Life's Simple 7 health factors AUC: 0.73, 95% CI: 0.72, 0.74 versus base model AUC: 0.68, 95% CI: 0.67, 0.69; P<0.001).
Number of Ideal Health Factors and Risk of Incident Chronic Kidney Disease
Approximately a third of study participants with 0 ideal health factors at baseline developed chronic kidney disease during follow‐up, whereas only 6.5% of those with 6 or 7 ideal health factors developed chronic kidney disease (Table 5). There was a graded relationship between number of ideal Life's Simple 7 health factors and risk of incident chronic kidney disease after adjusting for age, sex, race, and eGFR (Figure 2; P‐value for trend <0.001). Compared to 0 ideal health factors, having 6 or 7 health factors was associated with 81% reduced risk of chronic kidney disease (HR: 0.19, 95% CI: 0.12, 0.29).
Components of the Healthy Diet Score and Risk of Incident Chronic Kidney Disease
Of the 5 individual healthy diet score components, the largest proportions of the study population met the ideal criteria for self‐reported consumption of sugar‐sweetened beverages (75.1%) defined as ≤36 ounces per week (Table 6). Similar to the finding for the overall diet score, none of the individual components was significantly associated with risk of incident chronic kidney disease either in categorical or continuous analysis (all P‐values ≥0.09).
There was no evidence of effect modification by sex (P‐value for interaction >0.20) or racial group (P‐value for interaction >0.30).
Effects estimates were similar to the main results using several definitions for healthy diet score components: sugar‐sweetened beverages were restricted to regular soft drinks only; orange juice and grapefruit juice were included in the fruits and vegetables category; and white potatoes and sweet potatoes were removed from the fruits and vegetables category.
Using eGFR exclusively for the definition of chronic kidney disease, there were fewer cases and lower incidence rates, but relative risk estimates for chronic kidney disease by number of ideal Life's Simple 7 health factors were similar to those for the composite definition of chronic kidney disease (Table 7).
In this population‐based cohort study of individuals without kidney disease at baseline, the AHA's Life's Simple 7 healthy lifestyle metric was associated with reduced risk of incident chronic kidney disease even after accounting for demographic characteristics and baseline kidney function. In particular, not smoking, low body mass index, regular physical activity, normal blood pressure, and normal blood glucose levels were associated with a lower risk of chronic kidney disease; whereas a healthy dietary pattern and normal total cholesterol were not. None of the 5 components of the healthy diet score was significantly associated with chronic kidney disease. There was a strong inverse relationship between number of ideal health factors and the development of chronic kidney disease.
To the best of our knowledge, this is the first investigation of a combination of health factors as defined by AHA Life's Simple 7 and incident chronic kidney disease in a general population. Two studies have been published on Life's Simple 7 and kidney disease progression among individuals with impaired kidney function.11, 12 In a subset of participants in the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study with eGFR <60 mL/min per 1.73 m2 (n=3093), 160 end‐stage renal disease cases were observed over a median follow‐up of 4 years.11 Consistent with our findings, there was a graded relationship between number of ideal health factors and end‐stage renal disease risk (HR for 4 versus 0 or 1 ideal factors: 0.52, 95% CI: 0.27, 0.98). However, this relationship was no longer significant after adjusting for eGFR, whereas our results persisted. The attenuation of the association suggests that maintaining optimal levels of health factors and following a healthy lifestyle may be particularly effective for preventing disease before the onset of kidney impairment.
With respect to the individual health factors, as in the present analysis, the REGARDS study found significant protective effects associated with ideal categories of physical activity, blood pressure, and blood glucose, but not with blood cholesterol or diet. Our results and the REGARDS study are consistent with the considerable body of literature reporting no association between total blood cholesterol and chronic kidney disease risk, with the possible exception of triglycerides and high‐density lipoprotein cholesterol.22, 23, 24 Unlike our study, the risk of end‐stage renal disease was not significantly associated with body mass index or smoking.
In the Chronic Renal Insufficiency Cohort study, some of the Life's Simple 7 factors—smoking, physical activity, diet, and body mass index—were related to kidney disease progression.12 Among 3006 Chronic Renal Insufficiency Cohort study participants, there were 726 chronic kidney disease events over a median follow‐up period of 4 years. Similar to the present study and REGARDS, there was a significant association between physical activity and kidney disease risk (except after adjustment for eGFR), but not diet. Also consistent with our findings but in contrast to REGARDS, abstaining from cigarette smoking offered a significant protective effect against kidney disease. The number of ideal lifestyle factors was not related to chronic kidney disease progression in the Chronic Renal Insufficiency Cohort study. Paradoxically, the authors reported lower kidney disease risk with higher body mass index. There is substantial evidence supporting our result that lower body mass index is associated with reduced risk of chronic kidney disease, but there is some heterogeneity in the literature.25, 26, 27, 28 Some of the inconsistencies between studies may be due to differences in defining ideal levels of the Life's Simple 7 factors or differences in study populations (chronic kidney disease versus general population cohorts) with the potential for reverse causality in persons with prevalent chronic kidney disease.
There are some limitations to consider when interpreting our results. The observed lack of association between dietary factors and chronic kidney disease is likely due to imprecision and inaccuracies in estimating dietary intake. The food frequency questionnaire is not the ideal instrument for assessing dietary intake, especially sodium. Biomarkers of dietary intake, such as 24‐hour urinary sodium levels, were not available in this study. The specific diet factors and thresholds used to define a heart healthy diet may not have captured the diet characteristics that are relevant for kidney health. Another study limitation, as with any observational study, is the potential influence of residual confounding on the study results due to unmeasured and imprecisely measured confounders. However, the ARIC study cohort is well characterized and data have been collected by standardized procedures with rigorous quality control. There were substantial differences in baseline characteristics according to number of ideal Life's Simple 7 factors. These baseline characteristics and the strongest risk factors for chronic kidney disease were either incorporated in the Life's Simple 7 metric or included as covariates in the multivariable regression models. Another limitation is the assessment of Life's Simple 7 factors at a single time point, which reflects how this health promotion strategy would likely be implemented (ie, during a clinical encounter with a health professional).
Our study also has several strengths. The results were robust to different definitions and forms of the health factors (ie, categorical and continuous), and were consistent across sex and racial groups. The ARIC study population is large and diverse; thus, the results are broadly generalizable to adults in the United States. Given the extended follow‐up period, we were able to enumerate several thousand incident chronic kidney disease events in individuals free of kidney disease at baseline, whereas previous studies were limited to chronic kidney disease cohorts with fewer kidney disease events. We have provided a comprehensive assessment of all 7 health factors for the overall Life's Simple 7 metric and for each factor individually including the 5 components of the healthy diet score as they relate to chronic kidney disease risk.
In conclusion, the AHA Life's Simple 7 metric, developed to measure and promote cardiovascular health, predicts reduced risk of incident chronic kidney disease. Five of 7 Life's Simple 7 factors (not smoking, normal body mass index, regular physical activity, normal blood pressure, and normal blood glucose) were protective against kidney disease in a general population. Attainment of ideal cardiovascular health may also have substantial benefit for prevention of chronic kidney disease. Recommending these ideal health factors may be effective as a population‐wide chronic kidney disease preventive strategy.
Sources of Funding
The Atherosclerosis Risk in Communities (ARIC) study is carried out as a collaborative study supported by National Heart, Lung, and Blood Institute contracts (HHSN268201100005C, HHSN268201100006C, HHSN268201100007C, HHSN268201100008C, HHSN268201100009C, HHSN268201100010C, HHSN268201100011C, and HHSN268201100012C). Dr Crews is supported by grant K23 DK097184 from the National Institute of Diabetes and Digestive and Kidney Diseases.
The authors thank the staff and participants of the ARIC study for their important contributions. Some of the data reported here have been supplied by the US Renal Data System. The interpretation and reporting of these data are the responsibility of the authors and in no way should be seen as an official policy or interpretation of the US government.
Parts of this work were presented during an oral session at the American Heart Association Scientific Sessions, November 7–11, 2015 in Orlando, FL.
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