W2 - Physical activity, sedentary behaviour and physical health

Question 1

Describe relative risk

Answer 1

– A measure of the risk of a certain event happening in one group compared to another group.
- A relative risk of 1 = no difference between two groups in terms of their risk, based on whether or not they were exposed to a certain factor/behaviour.
- A relative risk > 1 indicates being exposed to a certain factor/behaviour increases risk, whereas a value lower than 1 indicates a decreased risk
- Relative risk of < 1 = there is a reduced risk as a result of a condition

Question 2

What is meant by hazard ratio?

Answer 2

interpreted the same way as RR, but applies when looking at mortality as an outcome

Question 3

Describe the relationship between physical fitness and all cause mortality

Answer 3

• Normal weight(fit) group were used as the comparison/reference group
  
  • Regardless of weight status, people that were physically fit showed a reduced risk of premature mortality
  • Increased premature mortality in obese compared to overweight & normal weight
  • Tells us that perhaps physical fitness is more important to health than a person’s weight status

Question 4

What was the relationship found between PA and CVD?

Answer 4

• Accelerometer measured physical activity and cardiovascular disease (CVD) incidence
  
  • 90,211 participants (mean age 62 yrs) without prior or concurrent CVD from the UK Biobank cohort, followed up over ~5 years (Ramakrishnan et al. 2021)
  • Linear relationship with increased PA and reduced risk of CVD (with both moderate & vigorous intensities)

Question 5

What association was seen between sitting and all-cause mortality?

Answer 5

Increased sitting is associated with increased all-cause mortality; risk mitigated in physically active people (Ekelund et al. 2016, n = 1,005,791)
- Those active for 60–75 mins/day seem to have no increased risk even if they sit for >8 hrs/day

- High PA group seem to have lower risk of premature mortality even when sitting > 8hrs per day

Question 6

How much time is too much to be sat?

How much sitting time a day was shown to increase mortality?

Answer 6

• Meta-analyses based on 1,331,468 participants
  
  • Independent of PA, total sitting and TV viewing time are associated with greater risk for several major chronic disease outcomes.
  • For all-cause and CVD mortality, a threshold of 6–8 hrs/day of total sitting and 3–4 hrs/day of TV viewing was identified, above which the risk is increased.
  • Dose-response relations between sedentary time and mortality increased from 7.5 to 9 hours, and were most pronounced at sitting times > 9.5 hours

Question 7

What is the needed amount of PA due to physical activity guidelines?

Answer 7

Adults should aim to minimise the amount of time spent being sedentary, and break up long periods of inactivity with at least light physical activity.

• 150 hrs per week of moderate PA
• 75 hrs of vigorous PA per week