What are the health implications of sedentary behavior in New Zealand?

Sedentary Behaviour in New Zealand: Definition and Health Implications

In New Zealand, sedentary behaviour is officially defined as "sit less" and "break up long periods of sitting" according to the 2015 New Zealand Ministry of Health guidelines. 1

Definition and Conceptualization

Sedentary behaviour in New Zealand follows two main conceptual frameworks:

1. Physiological definition: Activities with energy expenditure <1.5 metabolic equivalents (METs)
2. Postural and contextual definition: Activities that involve sitting or reclining posture during waking hours 1

It's important to note that these definitions are not always consistent. For example, some sitting activities like classroom sitting (1.8 METs) and driving (2.5 METs) exceed the 1.5 MET threshold but are still considered sedentary behaviours 1.

New Zealand's Official Guidelines on Sedentary Behaviour

The New Zealand Ministry of Health (2015) provides two key recommendations regarding sedentary behaviour:

• "Sit less"
• "Break up long periods of sitting" 1

Notably, these recommendations appear before physical activity recommendations in the New Zealand guidelines, highlighting their perceived importance 1. Unlike some countries that provide more detailed guidance, New Zealand's recommendations are non-quantitative and relatively simple.

Health Implications of Sedentary Behaviour

Cardiometabolic Health

Sedentary behaviour has been associated with increased risk of:

• Type 2 diabetes
• Cardiovascular disease
• Metabolic syndrome 1

However, the evidence base for these associations has limitations:

• Many studies use TV viewing as a proxy for sedentary behaviour, which may not accurately represent all forms of sitting 1
• The independence of sedentary behaviour from physical activity remains debated 1

Body Composition

Recent research in New Zealand populations shows:

• Replacing sedentary time with moderate-intensity physical activity predicted improvements in body composition metrics for Māori women (14.83% improvement in body fat percentage) and Pacific women (improved waist-to-hip and android-to-gynoid ratios) 2
• The benefits were greater when sedentary time was replaced with moderate-to-vigorous physical activity 2

Mental Health

For people with conditions like schizophrenia and major clinical depression, physical activity (as opposed to sedentary behaviour) has been associated with improved quality of life 1.

Population Differences in New Zealand

Sedentary behaviour patterns vary across different demographic groups in New Zealand:

• Children spend approximately 31.1% of their time in sedentary behaviours 3
• Significant variations exist across ethnic groups, gender, and household income levels 3
• Only 10.6% of New Zealand children meet the combined 24-hour Movement Guidelines (which include recommendations on physical activity, screen time, and sleep) 3

Emerging Understanding of Sedentary Behaviour

Recent research suggests that sedentary behaviour may be more than just physical inactivity:

• It may involve cognitive work that creates neurogenic stress 4
• Screen-based leisure activities and screen-based work activities may have different physiological effects 4
• Mental work during sedentary time may increase glycemic instability and food intake 4

Breaking Up Sedentary Time

The concept of "sedentary breaks" is emphasized in New Zealand guidelines, but the evidence supporting their health benefits is mixed:

• Cross-sectional studies show inconsistent associations between sedentary breaks and cardiometabolic markers 1
• Limited prospective evidence supports the health benefits of breaking up sedentary time 1
• The WHO guidelines suggest replacing sedentary time with any intensity of physical activity (including light intensity) has health benefits 1

Practical Recommendations

Based on the most recent evidence:

1. Reduce total sedentary time throughout the day
2. Break up prolonged periods of sitting with any form of physical activity
3. Replace sedentary time with at least moderate-intensity physical activity for optimal health benefits, especially for improving body composition and metabolic markers 2
4. Recognize that different forms of sedentary behaviour (e.g., TV viewing vs. computer work) may have different health implications 4

Common Pitfalls in Understanding Sedentary Behaviour

• Confusing sedentary behaviour with physical inactivity: They are related but distinct concepts
• Relying on TV viewing as a proxy for all sedentary behaviour: Different sedentary activities may have different health implications
• Assuming all sitting activities are below 1.5 METs: Some common sitting activities exceed this threshold
• Overlooking the potential cognitive/neurogenic aspects of sedentary behaviour beyond just lack of movement

The evidence on sedentary behaviour continues to evolve, with a need for more consistent definitions, better measurement methods, and stronger prospective studies using objective measures 5.