Interactive effects of physical fitness and body mass index on risk of stroke: A national cohort study

Association between baseline levels of muscular strength and risk of stroke in later life: The Cooper Center Longitudinal Study

BACKGROUND

Muscular strength is an important component of physical fitness. We evaluated the relationship between baseline muscular strength and risk of stroke among adults who were aged ≥65 years during follow-up.

METHODS

We included 7627 healthy adults (mean age = 43.9 years, 86.0% male) underwent a baseline physical examination between 1980 and 1989. Muscular strength was determined by 1-repetition maximum measures for bench press and leg press and categorized into age- and sex-specific tertiles for each measure. Cardiorespiratory fitness (CRF) was assessed via a maximal treadmill exercise test. Those enrolled in fee-for-service Medicare from 1999 to 2019 were included in the analyses. Associations between baseline strength and stroke outcomes were estimated using a modified Cox proportional hazards model. In a secondary analysis, we examined stroke risk by categories of CRF where Quintile 1 = low, Quintiles 2-3 = moderate, and Quintiles 4-5 = high CRF based on age and sex.

RESULTS

After 70,072 person-years of Medicare follow-up, there were 1211 earliest indications of incident stroke. In multivariable analyses, the hazard ratio (95% confidence interval (95%CI)) for stroke across bench press categories were 1.0 (referent), 0.96 (0.83-1.11), and 0.89 (0.77-1.04), respectively (p trend = 0.14). The trend across categories of leg press was also non-significant (p trend = 0.79). Adjusted hazard ratio (95%CI) for stroke across ordered CRF categories were 1.0 (referent), 0.90 (0.71-1.13), and 0.72 (0.57-0.92) (p trend < 0.01).

CONCLUSION

While meeting public health guidelines for muscular strengthening activities is likely to improve muscular strength as well as many health outcomes in older adults, performing such activities may not be helpful in preventing stroke. Conversely, meeting guidelines for aerobic activity is likely to improve CRF and lower stroke risk.

The association of adolescent fitness with cardiometabolic diseases in late adulthood: A 45-year longitudinal study

OBJECTIVES

The aim of this study was to examine the associations of adolescent cardiorespiratory fitness (CRF), muscular fitness (MF), and speed-agility fitness (SA) with middle-aged cardiometabolic disease risk and explore sex differences.

METHODS

This 45-year prospective cohort study examined the associations between objectively measured fitness at adolescence (12-19 years) and physician-ascertained diabetes mellitus, elevated blood pressure (BP), and coronary heart disease reported either in early (37-44 years) or late (57-64 years) middle age, and self-measurement of waist circumference (WC) in late middle age. Fitness measurements for healthy adolescents in baseline included CRF (1.5 km [girls] and 2 km [boys] run), MF (standing broad jump, sit-ups, pull-ups [boys], and flexed-arm hang [girls]), and SA (50 m dash and 4 × 10 m shuttle run). Logistic regression and general linear models were adjusted for baseline age, sex, and body mass index (BMI), involving data from baseline and at least one follow-up measurement (N up to 1358, 47% males).

RESULTS

Adolescent CRF was inversely, and regardless of adiposity, associated with middle age accumulated burden of cardiometabolic conditions in the whole sample (N = 562, ß = -0.10, 95% confidence intervals [CI] [-0.18, -0.03], p = 0.006), and elevated BP in females (N = 256, OR = 0.71, 95% CI [0.51, 0.91]). Overall, we observed stronger associations in females than in males. An inverse association of adolescent MF and SA with middle-aged WC was observed, but it did not show as consistent associations as with CRF.

CONCLUSIONS

In this study, adolescent fitness, particularly CRF, was inversely associated with the burden of cardiometabolic conditions up to 45 years. Promotion of fitness in youth may be beneficial in preventing adulthood cardiometabolic diseases.

High-intensity training in patients with lacunar stroke: A one-year follow-up

OBJECTIVES

Physical inactivity is a major risk factor for stroke. It is a challenge for patients to initiate and adhere to regular exercise post-stroke. Early initiation of home-based high-intensity interval training (HIIT) may engage patients in physical activity, improve cardiorespiratory fitness, and reduce risk of recurrent stroke.

MATERIALS AND METHODS

Post-intervention follow-up of patients with lacunar stroke, randomized to three-months HIIT including weekly motivational calls, or usual care. At follow-up (six- and 12-months post-stroke), we investigated changes in cardiorespiratory fitness, physical activity, fatigue, depression, mental well-being, stress, cognition, cardiovascular function, and recurrent stroke.

RESULTS

We included 71 patients of whom 59 patients (mean age: 63.9 ± 8.8 years) completed six- and 12-month follow-up. No change was detected in cardiorespiratory fitness between groups from baseline to 12-months follow-up. At six months, vigorous-intensity activity (median hours/week [interquartile range]) was maintained in the intervention group (baseline, 0[0;2]; post-intervention, 2[0;3]; six-month, 2[0;4]) and increased in the usual care group (baseline, 0[0;1]; post-intervention, 1[0;2]; six-month, 1[0;3]), with no difference between groups. Vigorous-intensity activity declined to baseline levels at 12-months in both groups. Secondary outcomes improved from baseline to 12-months with no significant differences between groups. Similar rate of recurrent stroke (n=3) occurred in each group with a three-month delay in the intervention group.

CONCLUSIONS

Early initiated HIIT did not increase long-term cardiorespiratory fitness, but increased time spent doing vigorous-intensity activities post-stroke. Decline to baseline activity level at 12 months warrants identification of motivators to initiate and sustain physical activity post-stroke.

The relationship between body mass index and stroke: a systemic review and meta-analysis

BACKGROUND

Stroke is an acute cerebrovascular event closely related to brain tissue damage, and is one of the major causes of death and disability in worldwide. Various studies have reported the effects of body mass index (BMI) on the risk of stroke, but the results remain varied and these results have not been synthesized. Therefore, a meta-analysis was performed to evaluate the relationship between BMI and the risk of stroke.

OBJECTIVES

This systematic review was conducted to explore the relationship between BMI and the risk of stroke.

METHODS

PubMed, EMBASE, Web of Science and Cochrane Library, China Knowledge Resource Integrated Database (CNKI), WanFang Database, Chinese Biomedical Database (CBM), and CQVIP were comprehensively searched for studies exploring the relationship between BMI and stroke from inception to December 1, 2021.

RESULTS

This review included 24 studies involving 5,798,826 subjects. The results of meta-analysis showed that the pooled RR of stroke risk was 0.93 (95% confidence interval [CI] 0.82-1.06, I² = 88.8%, P = 0.29) for the underweight group. Higher BMI (overweight or obese group) was associated with an increased overall risk of stroke, with pooled RR values of 1.25 (95% CI 1.16-1.34, I² = 84.8%, P = 0.00) and 1.47 (95% CI: 1.02-2.11, I² = 99.4%, P = 0.04).

CONCLUSION

The risk of stroke was positively correlated with BMI, and the association was stronger in male and ischemic stroke. Lowering BMI can be used as a way to prevent stroke, and for people who are overweight or obese, lowering body weight can reduce the risk of stroke.

Body Mass Index in 1.9 Million Adolescents and Stroke in Young Adulthood

[Figure: see text].

Childhood Risk Factors and Adulthood Cardiovascular Disease: A Systematic Review

OBJECTIVE

To conduct a comprehensive review of the literature on childhood risk factors and their associations with adulthood subclinical and clinical cardiovascular disease (CVD).

STUDY DESIGN

A systematic search was performed using the MEDLINE, EMBASE, PsycINFO, CINAHL, and Web of Science databases to identify English-language articles published through June 2018. Articles were included if they were longitudinal studies in community-based populations, the primary exposure occurred during childhood, and the primary outcome was either a measure of subclinical CVD or a clinical CVD event occurring in adulthood. Two independent reviewers screened determined whether eligibility criteria were met.

RESULTS

There were 210 articles that met the predefined criteria. The greatest number of publications examined associations of clinical risk factors, including childhood adiposity, blood pressure, and cholesterol, with the development of adult CVD. Few studies examined childhood lifestyle factors including diet quality, physical activity, and tobacco exposure. Domains of risk beyond "traditional" cardiovascular risk factors, such as childhood psychosocial adversity, seemed to have strong published associations with the development of CVD.

CONCLUSIONS

Although the evidence was fairly consistent in direction and magnitude for exposures such as childhood adiposity, hypertension, and hyperlipidemia, significant gaps remain in the understanding of how childhood health and behaviors translate to the risk of adulthood CVD, particularly in lesser studied exposures like glycemic indicators, physical activity, diet quality, very early life course exposure, and population subgroups.

Early-Life Cardiorespiratory Fitness and Long-term Risk of Prostate Cancer

BACKGROUND

Adolescence is a period of rapid prostatic growth, yet is understudied for susceptibility for future risk of prostate cancer. We examined cardiorespiratory fitness (CRF) in late adolescence in relation to long-term prostate cancer risk.

METHODS

A population-based cohort study was conducted of all 699,125 Swedish military conscripts during 1972-1985 (97%-98% of 18-year-old men) in relation to risk of prostate cancer overall, aggressive prostate cancer, and prostate cancer mortality during 1998-2017 (ages 50-65 years). CRF was measured by maximal aerobic workload, and prostate cancer was ascertained using the National Prostate Cancer Register. Muscle strength was examined as a secondary predictor.

RESULTS

In 38.8 million person-years of follow-up, 10,782 (1.5%) men were diagnosed with prostate cancer. Adjusting for sociodemographic factors, height, weight, and family history of prostate cancer, high CRF was associated with a slightly increased risk of any prostate cancer [highest vs. lowest quintile: incidence rate ratio (IRR), 1.10; 95% CI, 1.03-1.19; P = 0.008], but was neither significantly associated with aggressive prostate cancer (1.01; 0.85-1.21; P = 0.90) nor prostate cancer mortality (1.24; 0.73-2.13; P = 0.42). High muscle strength also was associated with a modestly increased risk of any prostate cancer (highest vs. lowest quintile: IRR, 1.14; 95% CI, 1.07-1.23; P < 0.001), but neither with aggressive prostate cancer (0.88; 0.74-1.04; P = 0.14) nor prostate cancer mortality (0.81; 0.48-1.37; P = 0.43).

CONCLUSIONS

High CRF or muscle strength in late adolescence was associated with slightly increased future risk of prostate cancer, possibly related to increased screening, but neither with risk of aggressive prostate cancer nor prostate cancer mortality.

IMPACT

These findings illustrate the importance of distinguishing aggressive from indolent prostate cancer and assessing for potential detection bias.

Independent and combined associations of cardiorespiratory fitness and muscle strength with metabolic syndrome in older adults: A cross-sectional study

BACKGROUND

Studies have shown that low cardiorespiratory fitness (CRF) and low muscle strength are independently associated with metabolic syndrome (MetS) in older adults. This study investigated the isolated and combined associations of low CRF and muscle strength with MetS in older adults.

METHODS

This cross-sectional study included 184 older adults (71% women; aged 65.6 ± 4.3 years) without a prior history of cardiovascular disease. CRF and muscle strength were assessed by the six-minute walking test and 30-s chair stand test, respectively. Results below the 25th percentile of the cohort were used to define low CRF and low muscle strength. MetS was defined according to NCEP-ATP III criteria. Poisson's regression with robust variance was used to determine the prevalence ratio (PR) for MetS. Reference group was composed by older adults with both CRF and muscle strength above 25th percentile.

RESULTS

Prevalence of low CRF, low muscle strength, and combined low CRF and muscle strength was 22.8%, 17.9%, and 10.9%, respectively. The prevalence of MetS was 56.5% in the full cohort. Isolated low CRF (PR 1.05, 95% CI 0.73 to 1.52; p = 0.793) and muscle strength (PR 1.09, 95% CI 0.74 to 1.61; p = 0.651) were not associated with MetS in the adjusted analysis. Combined low CRF and muscle strength was associated with MetS (PR 1.45, 95% CI 1.09 to 1.93; p = 0.011).

CONCLUSIONS

Older adults with combined, but not isolated, low CRF and muscle strength showed an increased risk for MetS.

Recurrent depression in childhood and adolescence and low childhood socioeconomic status predict low cardiorespiratory fitness in early adulthood

BACKGROUND

Cardiorespiratory fitness (CRF) strongly influences health, but very little is known about the childhood determinants of adult CRF. Our longitudinal study investigated whether childhood psychopathology and socioeconomic status (SES) were related to adult CRF in 1647 Finnish male military conscripts.

METHODS

Childhood psychopathology was assessed at the age of eight using the Rutter and Children's Depression Inventory questionnaires. Parental education and family structure were used to assess childhood SES. In late adolescence, depressive symptoms were assessed with the Beck Depression Inventory and smoking with a questionnaire. CRF in early adulthood was examined with the Cooper's 12-minute run test.

RESULTS

General linear models showed that low parental education (p=0.001), depressive symptoms in childhood (p=0.035) and late adolescence, smoking, underweight, and overweight/obesity (all p<0.001) independently predicted lower CRF. The interaction between depressive symptoms in childhood and adolescence was significant (p=0.003). In adolescents with depressive symptoms, childhood depressive symptoms (p=0.001) and overweight/obesity (p<0.001) predicted lower CRF. In adolescents without depressive symptoms, conduct problems in childhood predicted lower CRF in the initial models, but the effect disappeared after taking into account smoking and body mass index. Mediational analysis confirmed these results.

LIMITATIONS

We lacked data on physical activity and only studied males at three time-points.

CONCLUSIONS

Recurrent depression in childhood and adolescence and low SES in childhood predict lower adult CRF. Conduct problems in childhood predict lower CRF, but the effect is mediated by overweight/obesity and smoking. Psychiatric treatment for children and adolescents should promote physical activity, particularly for children with low SES.

Effects of Tai Chi on Cerebral Hemodynamics and Health-Related Outcomes in Older Community Adults at Risk of Ischemic Stroke: A Randomized Controlled Trial

This study investigated the effects of Tai Chi compared with no exercise control on the cerebral hemodynamic parameters and other health-related factors in community older adults at risk of ischemic stroke. A total of 170 eligible participants were randomly allocated to Tai Chi or control group. The cerebral hemodynamic parameters and physical fitness risk factors of cardiovascular disease were measured at baseline, 12 weeks, and 24 weeks. After the 12-week intervention, Tai Chi significantly improved the minimum of blood flow velocity (BFVmin); BFVmean; pulsatility index and resistance index of the right anterior cerebral artery; and BFVmax, BFVmin, and BFVmeanparameters of the right middle cerebral artery. Tai Chi training also decreased triglyceride, fasting blood glucose, and homocysteine levels, and improved balance ability. Therefore, the supervised 12-week Tai Chi exercise had potential beneficial effects on cerebral hemodynamics, plasma risk factors, and balance ability in older community adults at risk of ischemic stroke.

Exercise Is Medicine: Primary Care Counseling on Aerobic Fitness and Muscle Strengthening

Patient counseling on physical fitness remains underutilized in primary care, despite its clinical and cost effectiveness. Most counseling interventions have focused on aerobic activity and neglected another vital component of physical fitness, muscle strengthening, which has recently been shown to be independently protective against cardiometabolic diseases and premature mortality. This article reviews the latest scientific evidence and makes recommendations toward a more comprehensive approach for promoting physical fitness in primary care. Given the high prevalence and wide-ranging health impacts of physical inactivity, counseling on physical fitness should be a standard part of wellness promotion and disease prevention and treatment for all patients. Interventions that include muscle strengthening will have a significantly greater impact on health outcomes than those focused on aerobic fitness alone. Counseling to promote both aerobic fitness and muscle strengthening is indicated for all patients, irrespective of body weight, and should begin early in life and continue across the life course.

Associations between dietary risk factors and ischemic stroke: a comparison of regression methods using data from the Multi-Ethnic Study of Atherosclerosis

OBJECTIVES

We analyzed dietary patterns using reduced rank regression (RRR), and assessed how well the scores extracted by RRR predicted stroke in comparison to the scores produced by partial least squares and principal component regression models.

METHODS

Dietary data at baseline were used to extract dietary patterns using the 3 methods, along with 4 response variables: body mass index, fibrinogen, interleukin-6, and low-density lipoprotein cholesterol. The analyses were based on 5,468 males and females aged 45-84 years who had no clinical cardiovascular disease, using data from the Multi-Ethnic Study of Atherosclerosis.

RESULTS

The primary factor derived by RRR was positively associated with stroke incidence in both models. The first model was adjusted for sex and race and the second model was adjusted for the variables in model 1 as well as smoking, physical activity, family and sibling history of stroke, the use of any lipid-lowering medication, the use of any anti-hypertensive medication, hypertension, and history of myocardial infarction (model 1: hazard ratio [HR], 7.49; 95% confidence interval [CI], 1.66 to 33.69; p for trend=0.01; model 2: HR, 6.83; 95% CI, 1.51 to 30.87 for quintile 5 compared with the reference category; p for trend=0.02).

CONCLUSIONS

Based primarily on RRR, we identified that a dietary pattern high in fats and oils, poultry, non-diet soda, processed meat, tomatoes, legumes, chicken, tuna and egg salad, and fried potatoes and low in dark-yellow and cruciferous vegetables may increase the incidence of ischemic stroke.

Height, Weight, and Aerobic Fitness Level in Relation to the Risk of Atrial Fibrillation

Tall stature and obesity have been associated with a higher risk of atrial fibrillation (AF), but there have been conflicting reports of the effects of aerobic fitness. We conducted a national cohort study to examine interactions between height or weight and level of aerobic fitness among 1,547,478 Swedish military conscripts during 1969-1997 (97%-98% of all 18-year-old men) in relation to AF identified from nationwide inpatient and outpatient diagnoses through 2012 (maximal age, 62 years). Increased height, weight, and aerobic fitness level (but not muscular strength) at age 18 years were all associated with a higher AF risk in adulthood. Positive additive and multiplicative interactions were found between height or weight and aerobic fitness level (for the highest tertiles of height and aerobic fitness level vs. the lowest, relative excess risk = 0.51, 95% confidence interval (CI): 0.40, 0.62; ratio of hazard ratios = 1.50, 95% CI: 1.34, 1.65). High aerobic fitness levels were associated with higher risk among men who were at least 186 cm (6 feet, 1 inch) tall but were protective among shorter men. Men with the combination of tall stature and high aerobic fitness level had the highest risk (for the highest tertiles vs. the lowest, adjusted hazard ratio = 1.70, 95% CI: 1.61, 1.80). These findings suggest important interactions between body size and aerobic fitness level in relation to AF and may help identify high-risk subgroups.

The association of cardiorespiratory fitness with cardiometabolic factors, markers of inflammation, and endothelial dysfunction in Latino youth: findings from the Hispanic Community Children's Health Study/Study of Latino Youth

PURPOSE

To evaluate the relationship of cardiorespiratory fitness (CRF) with cardiovascular disease risk factors and a biomarker of endothelial dysfunction (e-selectin) among Hispanic/Latino youth.

METHODS

The study included 1380 Hispanic/Latino youths (8-16 years old) from the Hispanic Community Children's Health Study/Study of Latino Youth that enrolled from four cities (Bronx, Chicago, Miami, and San Diego). CRF was assessed by a 3-minute step test that uses postexercise heart rate to estimate maximal oxygen uptake. Regression models assessed differences in cardiometabolic markers across quartiles of CRF, adjusting for potential confounders.

RESULTS

CRF was higher among boys (mean: 57.6 mL per kg/min, 95% confidence interval, 56.8-58.4) compared to girls (mean: 54.7 mL per kg/min, 95% confidence interval, 53.9-55.5). Higher levels of CRF were associated with more favorable levels of cardiometabolic, inflammation, and endothelial dysfunction factors (P-values <.001) and independently of physical activity and sedentary time. Compared to the lowest quartile of CRF, the odds of having greater than or equal to two cardiovascular disease risk factors was lower at higher quartiles of CRF, after adjustment for potential confounders.

CONCLUSIONS

Among Hispanic/Latino youth, CRF appears to be a strong protective factor for endothelial dysfunction and cardiometabolic risk factors. Strategies to improve CRF may be a useful approach for improving cardiovascular health in youth.

Cardiorespiratory Fitness Cutoff Points for Early Detection of Present and Future Cardiovascular Risk in Children: A 2-Year Follow-up Study

OBJECTIVE

To examine the association between cardiorespiratory fitness (CRF) at baseline and cardiovascular disease (CVD) risk in 6- to 10-year-olds (cross-sectional) and 2 years later (8- to 12-year-olds [longitudinal]) and whether changes with age in CRF are associated with CVD risk in children aged 8 to 12 years.

PATIENTS AND METHODS

Spanish primary schoolchildren (n=236) aged 6 to 10 years participated at baseline. Of the 23 participating primary schools, 22% (n=5) were private schools and 78% (n=18) were public schools. The dropout rate at 2-year follow-up was 9.7% (n=23). The 20-m shuttle run test was used to estimate CRF. The CVD risk score was computed as the mean of 5 CVD risk factor standardized scores: sum of 2 skinfolds, systolic blood pressure, insulin/glucose, triglycerides, and total cholesterol/high-density lipoprotein cholesterol.

RESULTS

At baseline, CRF was inversely associated with single CVD risk factors (all P<.05) and CVD risk score at baseline and follow-up (P<.001). Cardiorespiratory fitness cutoff points of 39.0 mL/kg per minute or greater in boys and 37.5 mL/kg per minute or greater in girls are discriminative to identify CVD risk in childhood (area under the curve, >0.85; P<.001) and to predict CVD risk 2 years later (P=.004). Persistent low CRF or the decline of CRF from 6-10 to 8-12 years of age is associated with increased CVD risk at age 8 to 12 years (P<.001).

CONCLUSION

During childhood, CRF is a strong predictor of CVD risk and should be monitored to identify children with potential CVD risk.

Aerobic fitness, muscular strength and obesity in relation to risk of heart failure

OBJECTIVE

Low physical fitness and obesity have been associated with higher risk of developing heart failure (HF), but their interactive effects are unknown. Elucidation of interactions among these common modifiable factors may help facilitate more effective primary prevention.

METHODS

We conducted a national cohort study to examine the interactive effects of aerobic fitness, muscular strength and body mass index (BMI) among 1 330 610 military conscripts in Sweden during 1969-1997 (97%-98% of all 18-year-old men) on risk of HF identified from inpatient and outpatient diagnoses through 2012 (maximum age 62 years).

RESULTS

There were 11 711 men diagnosed with HF in 37.8 million person-years of follow-up. Low aerobic fitness, low muscular strength and obesity were independently associated with higher risk of HF, after adjusting for each other, socioeconomic factors, other chronic diseases and family history of HF. The combination of low aerobic fitness and low muscular strength (lowest vs highest tertiles) was associated with a 1.7-fold risk of HF (95% CI 1.6 to 1.9; p<0.001; incidence rates per 100 000 person-years, 43.2 vs 10.8). These factors had positive additive and multiplicative interactions (p<0.001) and were associated with increased risk of HF even among men with normal BMI.

CONCLUSIONS

Low aerobic fitness, low muscular strength and obesity at the age of 18 years were independently associated with higher risk of HF in adulthood, with interactive effects between aerobic fitness and muscular strength. These findings suggest that early-life interventions may help reduce the long-term risk of HF and should include both aerobic fitness and muscular strength, even among persons with normal BMI.

Interactive Effects of Aerobic Fitness, Strength, and Obesity on Mortality in Men

INTRODUCTION

Low aerobic fitness, low muscular strength, and obesity have been associated with premature mortality, but their interactive effects are unknown. This study examined interactions among these common, modifiable factors, to help inform more-effective preventive interventions.

METHODS

This national cohort study included all 1,547,478 military conscripts in Sweden during 1969-1997 (97%-98% of all men aged 18 years each year). Aerobic fitness, muscular strength, and BMI measurements were examined in relation to all-cause and cardiovascular mortality through 2012 (maximum age, 62 years). Data were collected/analyzed in 2015-2016.

RESULTS

Low aerobic fitness, low muscular strength, and obesity at age 18 years were independently associated with higher all-cause and cardiovascular mortality in adulthood. The combination of low aerobic fitness and muscular strength (lowest versus highest tertiles) was associated with twofold all-cause mortality (adjusted hazard ratio=2.01; 95% CI=1.93, 2.08; p<0.001; mortality rates per 100,000 person years, 247.2 vs 73.8), and 2.6-fold cardiovascular mortality (2.63; 95% CI=2.38, 2.91; p<0.001; 43.9 vs 8.3). These factors also had positive additive and multiplicative interactions in relation to all-cause mortality (their combined effect exceeded the sum or product of their separate effects; p<0.001), and were associated with higher mortality even among men with normal BMI.

CONCLUSIONS

Low aerobic fitness, low muscular strength, and obesity at age 18 years were associated with increased mortality in adulthood, with interactive effects between aerobic fitness and muscular strength. Preventive interventions should begin early in life and include both aerobic fitness and muscular strength, even among those with normal BMI.

Interactive effects of obesity and physical fitness on risk of ischemic heart disease

Background/Objectives

Obesity and low physical fitness are known risk factors for ischemic heart disease (IHD), but their interactive effects are unclear. Elucidation of interactions between these common, modifiable risk factors may help inform more effective preventive strategies. We examined interactive effects of obesity, aerobic fitness, and muscular strength in late adolescence on risk of IHD in adulthood in a large national cohort.

Subjects/Methods

We conducted a national cohort study of all 1,547,407 military conscripts in Sweden during 1969–1997 (97–98% of all 18-year-old males each year). Aerobic fitness, muscular strength, and body mass index (BMI) measurements were examined in relation to IHD identified from outpatient and inpatient diagnoses through 2012 (maximum age 62 years).

Results

There were 38,142 men diagnosed with IHD in 39.7 million person-years of follow-up. High BMI or low aerobic fitness (but not muscular strength) was associated with higher risk of IHD, adjusting for family history and socioeconomic factors. The combination of high BMI (overweight/obese vs. normal) and low aerobic fitness (lowest vs. highest tertile) was associated with highest IHD risk (incidence rate ratio, 3.11; 95% CI, 2.91–3.31; P<0.001). These exposures had no additive and a negative multiplicative interaction (i.e., their combined effect was less than the product of their separate effects). Low aerobic fitness was a strong risk factor even among those with normal BMI.

Conclusions

In this large cohort study, low aerobic fitness or high BMI at age 18 was associated with higher risk of IHD in adulthood, with a negative multiplicative interaction. Low aerobic fitness appeared to account for a similar number of IHD cases among those with normal vs. high BMI (i.e., no additive interaction). These findings suggest that interventions to prevent IHD should begin early in life and include not only weight control but aerobic fitness, even among persons of normal weight.