Cardiovascular–kidney–metabolic (CKM) syndrome is a recently defined clinical construct that integrates cardiovascular disease, chronic kidney disease, diabetes, hypertension, dyslipidaemia, and obesity into a unified risk continuum. The syndrome progresses through stages from early metabolic dysfunction to overt cardiovascular disease and advanced kidney disease. As CKM stage increases, mortality rises steeply.
Current physical activity guidelines prioritise moderate-to-vigorous physical activity (MVPA), typically recommending at least 150 minutes per week. However, many people with advanced CKM syndrome, particularly those with cardiovascular disease, diabetes complications, or chronic kidney disease, are unable to achieve or sustain such intensity. In real life, the vast majority of their movement consists of light-intensity activities such as slow walking, housework, food preparation, or moving around the home. Despite this, light physical activity (light PA) is rarely emphasised in guidelines or studied as a distinct exposure, particularly in people with established cardiometabolic or renal disease.
In a recent study, the authors aimed to determine whether light PA is associated with lower all-cause mortality across the full spectrum of CKM stages. The study used data from the US National Health and Nutrition Examination Survey (NHANES) 2003–2006, linked to mortality follow-up through 31 December 2019. The analysis included 7,246 adults aged 20 years or older who were capable of walking and had valid accelerometer data. Participants wore a hip-mounted ActiGraph AM-7164 accelerometer for between 1 and 7 valid days.
Physical activity was classified minute-by-minute using established cut-points into light PA and MVPA. Light PA and MVPA were summed to give total active time.
CKM stages were defined using questionnaire responses, physical measurements, and laboratory values, following established criteria:
- Stage 0: Normal weight, blood pressure, lipids, glycaemia, and kidney function
- Stage 1: Overweight or obesity (BMI ≥25), excess waist circumference, or prediabetes
- Stage 2: Diabetes, hypertension, metabolic syndrome, hypertriglyceridaemia, or moderate-to-high-risk chronic kidney disease
- Stage 3: Very high-risk chronic kidney disease or a ≥20% 10-year predicted cardiovascular risk
- Stage 4: Established cardiovascular disease
The weighted mean age of participants was 48 years, and 52% were women. Light PA and MVPA were only modestly correlated across CKM stages, indicating that light activity captures a distinct behavioural dimension rather than simply reflecting more vigorous exercise.
Median daily light PA declined steadily with worsening CKM stage:
- Stage 0/1: 4.8 hours per day
- Stage 4: 3.5 hours per day
However, light PA accounted for the overwhelming majority of all activity in every group. Across all CKM stages, at least 93.8% of total active time was light PA, rising to over 98.5% in stages 3 and 4. In other words, people with advanced disease were almost entirely reliant on light-intensity movement for their physical activity.
Over a median follow-up of 14.4 years, 1,799 deaths occurred. Mortality rates increased dramatically with CKM stage:
- Stage 0/1: 3.3 deaths per 1,000 person-years
- Stage 2: 10.5 per 1,000
- Stage 3: 74.9 per 1,000
- Stage 4: 70.7 per 1,000
After adjustment for demographics and MVPA, light PA was significantly associated with lower mortality in CKM stages 2, 3, and 4. For each additional 1 hour per day of light PA, mortality risk was reduced by approximately 14% to 20%, depending on CKM stage. These associations were seen even after accounting for whether people met MVPA guidelines, indicating that light activity provides independent benefit beyond structured exercise.
While relative risk reductions were similar across stages, the absolute benefit of light PA was much larger in people with more advanced disease, because their baseline mortality was so high.
For example, increasing daily active time from 1.5 to 2 hours was associated with:
- 2.2% lower absolute mortality risk in CKM stage 2
- 4.2% lower absolute mortality risk in CKM stage 4
Thus, modest increases in light activity yielded disproportionately large survival benefits in people with overt cardiovascular disease.
These findings align with randomised trials showing that exercise-based cardiac rehabilitation reduces cardiovascular mortality in patients with coronary heart disease. However, this study extends that evidence by showing that light-intensity activity, the dominant form of movement in daily life, also carries meaningful survival benefit, especially in high-risk individuals.
The results are particularly important because patients with CKM stages 3 and 4 often cannot tolerate vigorous exercise. For them, encouraging more light movement—walking slowly, standing up more often, doing household tasks, or simply reducing sitting time—may be both feasible and clinically impactful.
Source: Journal of the American Heart Association
Image Credit: iStock
