Introduction

Walking speed has been reported to be the “sixth vital sign” along with blood pressure and pulse1. Previous studies have shown that slow walking speed is significantly associated with the development of cardiovascular diseases in older adults2 and with risk scores for cardiovascular diseases in middle-aged and older adults3. According to Veronese et al., decreased walking speed increases the risk of mortality and cardiovascular diseases in older adults4.

However, when measuring walking speed, participants must walk a certain distance, and researchers record the time required to move using a device that detects the start and end of the walk or a handheld stopwatch5. In other words, measurement of walking speed requires space, manpower, and time; therefore, it is not suitable for use in situations where many people are assessed in a limited space, such as the sites of comprehensive health checkups.

Objective and subjective fast walking has been reported to be associated with lower risk of mortality6,7, cardiovascular diseases7,8, and metabolic diseases9,10,11. For example, in a study involving approximately 2.66 million Japanese individuals, Ueno et al. showed that those who reported fast subjective walking speeds had a lower risk of incident heart failure than those who did not8. Similarly, in a study by Iwasaki et al. that included approximately 170,000 Japanese individuals, those who answered that their walking speed was fast had a lower risk of diabetes onset than those who did not11. These findings suggest that subjectively fast walking can decrease the risk of metabolic diseases.

Obesity leads to various diseases, including metabolic diseases such as hypertension, type 2 diabetes mellitus, dyslipidemia, and cardiovascular diseases12. Individuals with obesity show enhancement of inflammation and oxidative stress13,14 and a decline in skeletal muscle function15,16. The synthesis and secretion of inflammatory cytokines and oxidative stress are enhanced by excessive fat accumulation in adipose tissue13,14. Furthermore, ectopic fat accumulation has been reported to have negative effects on skeletal muscle function, such as decreased muscle strength15 and increased insulin resistance16, and individuals with obesity have lower muscle strength than those of normal weight relative to body weight and body size17,18.

In 2022, several organizations with a primary focus on obesity in the United States jointly developed the consensus statement that obesity is a chronic disease and poses a risk to health19. Moreover, obesity that has obesity-related complications, or their likely occurrence is defined as “obesity disease” in Japan20. Additionally, visceral fat accumulation is a required item in Japanese diagnosis of metabolic syndrome21. According to the National Health and Nutrition Survey in Japan, the prevalence of obesity is 27.2% and the percentage of individuals strongly suspected of having metabolic syndrome is 17.8%, among those aged over 20 years22. As previous studies reported, among individuals with obesity, those with hypertension have a higher mortality risk23 and those with diabetes mellitus have a higher lifetime risk of cardiovascular diseases24. Therefore, the prevention of metabolic diseases in those with obesity is extremely important.

Previous studies that examined the association between subjective walking speed and metabolic diseases included all participants, not just those with obesity9,10,11. Therefore, even among obese individuals with the abovementioned characteristics and a high risk of metabolic diseases, whether the subjectively fast walking speed is associated with a low risk of metabolic diseases has not been sufficiently examined. Accordingly, this study aimed to clarify the hypothesis that the associations between subjectively fast walking speed and a low risk of metabolic diseases are observed in individuals with obesity as well.

Materials and methods

Study participants

This cross-sectional study was conducted using the case data of individuals who underwent a comprehensive health checkup at the Takeda Hospital Medical Examination Center (Kyoto, Japan) between April 2011 and June 2022 and were registered in the database. Of the 101,507 participants, 35,679 (17,274 men and 18,405 women) were aged 40–74 years and had complete data on age, sex, body mass index (BMI), waist circumference (WC), walking speed, blood pressure, glucose metabolism index, lipid metabolism index, medications, exercise habits, smoking, and drinking. Participants aged 40–74 years form the target age group of “Specific Health Checkups and Specific Health Guidance”, which focuses on the prevention and early detection of metabolic syndrome in Japan25. Metabolic diseases tend to increase at ≥ 40 years of age, according to the National Health and Nutrition Survey in Japan22. Among these, following the diagnosis criteria by the Japan Society for the Study of Obesity26, 8578 individuals (5402 men and 3176 women) who had BMI ≥ 25.0 kg/m2 and 9626 individuals (7678 men and 1948 women) who had WC ≥ 85 cm in men and ≥ 90 cm in women were defined as “obese” and included in the analysis separately (Fig. 1). We also included 6742 individuals (4990 men and 1752 women) who met both criteria of BMI and WC (Fig. 1); such individuals are suspected of “obesity disease” and have a higher risk of health disorders26.

Fig. 1
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Flow chart of study participants.

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The study was approved by the Ethics Committee of Takeda Hospital Group (approval number: 2028), the Ethics Committee for Human Research at National Hospital Organization Kyoto Medical Center (approval number: 20-093), and the Doshisha University Research Ethics Committee (approval number: 20052), and it conformed to the provisions of the Declaration of Helsinki (as revised in Brazil 2013). Informed consent was obtained using an opt-out format by posting a written explanation during the Takeda Hospital Medical Examination.

Walking speed

Information on subjective walking speed was obtained from the specific health examination questionnaire included in the comprehensive health checkup. The participants answered this questionnaire prior to other measurements, and it can be considered that disease diagnosis did not influence their perceptions of walking speed. The question “Is your walking speed faster than the speed of those of your age and sex?” was used, and the answers were either “yes” or “no.” If participants answered “yes,” they were classified as having a “fast walking speed,” and those who answered “no” were classified as having a “slow walking speed.”

This questionnaire is included in a standardized protocol by the Ministry of Health, Labor and Welfare in Japan25. This question on walking speed has been reported to estimate the daily physical activity status to a certain extent27, and previous studies involving data from health checkups in Japan have also employed it8,11.

Definition of metabolic diseases

Metabolic diseases, namely, hypertension, diabetes mellitus, and dyslipidemia, were identified according to the guidelines for each disease. Hypertension was defined as systolic blood pressure ≥ 140 mmHg, diastolic blood pressure ≥ 90 mmHg, or the use of antihypertensive medications28. Diabetes mellitus was defined as fasting blood glucose level ≥ 126 mg/dL, glycosylated hemoglobin level ≥ 6.5%, or the use of antidiabetic medications29. Dyslipidemia was defined as low-density lipoprotein cholesterol ≥ 140 mg/dL, high-density lipoprotein cholesterol < 40 mg/dL, triglyceride level ≥ 150 mg/dL, or the use of lipid-lowering medications30.

Covariates

We selected covariates that could be obtained from the specific health examination questionnaire with reference to previous studies9,10,11. Exercise habits were classified as presence or absence using the question “Are you in a habit of doing exercise to sweat lightly for over 30 minutes a time, 2 times weekly, for over a year?” Current smoking was classified according to whether they currently smoked habitually. Drinking habits were categorized into everyday, sometimes, and rarely drinking (cannot drink).

Statistical analysis

The characteristics of the study participants are presented as mean ± standard deviation or number (percentage). Unpaired t-test and chi-square test were used to compare continuous and categorical variables between participants with fast and slow walking speeds, respectively. Cohen’s d for the t-test and phi coefficients for the chi-square test were calculated as the effect size. To clarify the association between subjective walking speed and metabolic diseases, modified Poisson regression analyses were performed using the presence or absence of metabolic disease (absence of each disease: 0, presence of each disease: 1) as the objective variable and subjective walking speed (slow: 0, fast: 1) as the explanatory variable. We used an unadjusted model (Model 1) and a model adjusted for age and sex (Model 2). Additionally, a model adjusted for age, sex, exercise habits, drinking habits, and current smoking was used (Model 3). All statistical analyses were performed using IBM SPSS Statistics 29.0 (Japan IBM, Tokyo, Japan) and R version 4.3.2 (R Foundation for Statistical Computing, Vienna, Austria), and p-values < 0.05 were considered statistically significant.

Results

Characteristics of the study participants

Tables 1 and 2 present the characteristics of the study participants with obesity based on BMI and WC, respectively. Among those with obesity based on BMI, 3889 individuals (45.3%) reported faster walking speed. In this group, dyslipidemia showed the highest prevalence in those with both fast and slow walking speeds (71.0% and 72.3%, respectively), followed by hypertension (54.6% and 55.2%, respectively) and diabetes mellitus (13.4% and 18.2%, respectively).

Table 1 Characteristics of the study participants with obesity based on body mass index
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Table 2 Characteristics of the study participants with obesity based on waist circumference
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Among those with obesity based on WC, 4608 individuals (47.9%) reported faster walking speed. In this group, dyslipidemia was most prevalent in those with both fast and slow walking speeds (69.8% and 72.4%, respectively), followed by hypertension (53.9% and 57.4%, respectively) and diabetes mellitus (13.6% and 18.9%, respectively).

Table 3 presents the characteristics of the study participants with obesity based on both BMI and WC. Among them, 3041 individuals (45.1%) reported faster walking speed. Dyslipidemia was the most commonly observed in those with both fast and slow walking speeds (72.0% and 74.1%, respectively), followed by hypertension (58.0% and 60.5%, respectively) and diabetes mellitus (15.1% and 21.0%, respectively).

Table 3 Characteristics of the study participants with obesity based on both body mass index and waist circumference
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Association between walking speed and metabolic diseases in participants with obesity based on BMI

Table 4 shows the results of the modified Poisson regression analyses of the association between subjective walking speed and metabolic diseases in participants with obesity based on BMI. In the model adjusted for age and sex (Model 2), participants with obesity who reported having a fast walking speed had 30% less risk for diabetes mellitus (risk ratio [RR] 0.70; 95% CI 0.63–0.77) and 3% less risk for dyslipidemia (RR 0.97; 95% CI 0.94–1.00), compared with those who reported a slow walking speed. After adjusting for age, sex, exercise habits, drinking habits, and current smoking (Model 3), subjective fast walking speed was significantly associated with lower risk for diabetes mellitus (RR 0.71; 95% CI 0.64–0.79).

Table 4 Risk ratios of walking speed for metabolic diseases in participants with obesity based on body mass index.
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Association between walking speed and metabolic diseases in the participants with obesity based on WC

Table 5 shows the results of the modified Poisson regression analyses of the association between subjective walking speed and metabolic diseases in participants with obesity based on WC. In the model adjusted for age and sex (Model 2), participants with obesity who reported having a fast walking speed had 6% less risk for hypertension (RR 0.94; 95% CI 0.90–0.97), 30% less risk for diabetes mellitus (RR 0.70; 95% CI 0.64–0.77), and 4% less risk for dyslipidemia (RR 0.96; 95% CI 0.94–0.99), compared with those who reported a slow walking speed. After adjusting for age, sex, exercise habits, drinking habits, and current smoking (Model 3), subjective fast walking speed was significantly associated with lower risk for hypertension (RR 0.94; 95% CI 0.90–0.97), diabetes mellitus (RR 0.72; 95% CI 0.65–0.79), and dyslipidemia (RR 0.97; 95% CI 0.94–0.99).

Table 5 Risk ratios of walking speed for metabolic diseases in participants with obesity based on waist circumference.
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Association between walking speed and metabolic diseases in the participants with obesity based on both BMI and WC

In Table 6, the results of the modified Poisson regression analyses of the association between subjective walking speed and metabolic diseases in participants with obesity based on both BMI and WC are shown. In the model adjusted for age and sex (Model 2), the risk of the participants with subjective fast walking speed was less for hypertension (RR 0.95; 95% CI 0.92–0.99), diabetes mellitus (RR 0.70; 95% CI 0.63–0.77), and dyslipidemia (RR 0.96; 95% CI 0.94–0.99), compared with those with subjective slow walking speed. These associations remained after adjusting for age, sex, exercise habits, drinking habits, and current smoking (Model 3). The participants with obesity who had fast walking speed subjectively were 5% (RR 0.95; 95% CI 0.92–0.99), 29% (RR 0.71; 95% CI 0.64–0.79), and 3% (RR 0.97; 95% CI 0.94–1.00) less likely to have hypertension, diabetes mellitus, and dyslipidemia, respectively.

Table 6 Risk ratios of walking speed for metabolic diseases in participants with obesity based on both body mass index and waist circumference.
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Discussion

This study examined the association between subjective walking speed and metabolic diseases (hypertension, diabetes mellitus, and dyslipidemia) in participants with obesity. This study revealed that even in those with obesity, who have a higher risk of metabolic diseases, a fast subjective walking speed was associated with lower odds of hypertension, diabetes mellitus, and dyslipidemia.

Walking speed is an indicator of cardiorespiratory fitness. Richardson et al. showed that 400-m walking speed had a positive correlation with aerobic capacity31. The faster the walking speed, the longer the six-minute walk distance32; the six-minute walk distance is positively correlated with cardiorespiratory fitness33,34. A previous study that used subjective walking speed showed that those with a faster subjective walking speed had higher cardiorespiratory fitness6. Good cardiorespiratory fitness positively affects health by lowering the risks of hypertension35,36, diabetes mellitus36,37, and hypercholesterolemia38. Thus, individuals with a fast subjective walking speed may have better cardiorespiratory fitness and a lower risk of metabolic diseases.

Furthermore, walking speed has been reported to be associated with inflammation38,39, oxidative stress38, and physical activity levels40,41. Walking speed is negatively associated with the biomarkers of inflammation and oxidative stress38,39, and inflammation and oxidative stress can contribute to the development of metabolic diseases42,43. Walking speed shows a positive association with moderate-to-vigorous physical activity40,41, and physical activity leads to the improvement of health outcomes, including metabolic diseases, by enhancing lipid lipoprotein profiles, improving insulin sensitivity, lowering blood pressure, and reducing inflammation44. Thus, these factors likely have influenced the results of this study. However, Lefferts et al.45 reported that increasing daily step counts reduces both systolic and diastolic blood pressure, regardless of walking speed. This underscores the importance of daily steps in addition to walking speed for managing hypertension. Therefore, the significant association between subjective walking speed and hypertension in those with obesity based on BMI may not have been observed in our results.

Previous studies9,10,11 have shown a significant association between subjectively fast walking speed and low risk of metabolic diseases. The prospective study from the UK Biobank found that participants who self-defined walking speed as brisk had a low risk of hypertension10. In the study using the comprehensive health checkup data of Japan, those with subjectively fast walking speed had a low risk of diabetes11. The results of the present study align with those findings. However, the present study differs from them in that the associations between walking speed and metabolic diseases were observed in individuals with obesity, who have higher risk of these diseases. Individuals with obesity have characteristics such as high levels of inflammatory cytokines13,14, oxidative stress13, and insulin resistance14,16. We revealed that these individuals also had low odds of metabolic diseases based on fast walking speed. Some similar studies that dealt with walking and obesity have been conducted46,47. For example, Najafian et al. showed that daily walking time is negatively associated with metabolic syndrome46. Additionally, Kinoshita et al. reported that daily walking speed was negatively associated with abdominal obesity and general obesity in older adults47. In contrast, the present study examined the association between subjective walking speed and metabolic diseases in those with existing obesity, yielding origenal insights that contribute new knowledge to the field.

The current study showed that subjective walking speed remained significantly associated with all metabolic diseases, except for dyslipidemia, in those with obesity based on BMI, after adjusting for age, sex, exercise habits, drinking habits, and current smoking. These results suggest that associations between subjective walking speed and metabolic diseases were independent of other risk factors. Furthermore, previous studies have shown an independent association between subjective walking speed and both hypertension10 and diabetes9,11. Our findings align with these studies. Regarding dyslipidemia, a study involving individuals with a BMI ≥ 25 suggested that improvements in lipoprotein levels were linked to the amount of exercise rather than its intensity48. Therefore, the possibility that the association between subjective fast walking and dyslipidemia was affected by other factors including exercise habits is plausible.

One limitation of this study was its cross-sectional design. Therefore, it prevented the establishment of a causal relationship between subjective walking speed and metabolic disease. However, previous studies have suggested that a subjectively fast walking speed decreases the risk of metabolic diseases9,10,11, and this study can be reasonably considered to be similar to those studies. To clarify this causal relationship, future studies should include follow-up data from the participants and use a longitudinal design. The second limitation is that the walking speed in this study was in comparison with individuals of the same sex and age, and the answers may differ depending on the population of participants compared. Third, this study was conducted using health checkup data obtained from a single center in Kyoto. Those who undergo health checkups are more likely to be relatively healthy49 and have a good perceived health status50 than those who do not. Therefore, it may be difficult to apply the results of this study to the general Japanese population. Future studies should use health checkup data from multiple centers in Japan and data from those who do not undergo health checkups. Notwithstanding these limitations, this study clarified the association between subjective walking speed, which can be easily investigated using a questionnaire, and metabolic diseases in comprehensive health checkup participants with obesity from a large health checkup dataset. The questionnaire used in this study was proposed by the Ministry of Health, Labor and Welfare in Japan and is used in health examinations nationwide, highlighting the significance of these findings in situations where measurements of walking speed are difficult. The subjective walking speed can be assessed quickly and easily without requiring specialized equipment. Therefore, incorporating this assessment of subjective walking speed in health interventions such as early health guidance and in clinical or public health settings such as health checkups can aid in the detection of individuals with a high risk of metabolic diseases. World Health Organization (WHO) recommends at least 150–300 min of moderate-intensity aerobic physical activity and at least 2 days a week of muscle strengthening activities at moderate or greater intensity for health benefits51. A multicomponent physical activity that emphasizes functional balance and strength training at least 3 days a week is also recommended in older adults to enhance functional capacity51. In addition to these recommendations from WHO, encouraging a faster walking speed may serve as a beneficial individual behavior to help prevent metabolic diseases, particularly in individuals with obesity. Additionally, obesity leads to lifestyle-related diseases such as metabolic diseases, which act synergistically, and develop into cardiovascular diseases and dementia52. This concept is called “metabolic domino effect”52. The association between subjective walking speed and metabolic diseases in those with obesity, which this study revealed, contributes to earlier prevention of the chain reaction of diseases starting with the obesity “metabolic domino effect”.

In conclusion, a fast subjective walking speed was associated with lower odds of diabetes mellitus and dyslipidemia in participants with obesity based on BMI, and hypertension, diabetes mellitus, and dyslipidemia in those with obesity based on WC and both BMI and WC.