title: Is exercise protective against influenza-associated mortality?
abstract: BACKGROUND
  Little is known about the effect of physical exercise on influenza-associated mortality.
  
  
  RESULTS
  We collected information about exercise habits and other lifestyles, and socioeconomic and demographic status, the underlying cause of death of 24,656 adults (21% aged 30-64, 79% aged 65 or above) who died in 1998 in Hong Kong, and the weekly proportion of specimens positive for influenza A (H3N1 and H1N1) and B isolations during the same period. We assessed the excess risks (ER) of influenza-associated mortality due to all-natural causes, cardiovascular diseases, or respiratory disease among different levels of exercise: never/seldom (less than once per month), low/moderate (once per month to three times per week), and frequent (four times or more per week) by Poisson regression. We also assessed the differences in ER between exercise groups by case-only logistic regression. For all the mortality outcomes under study in relation to each 10% increase in weekly proportion of specimens positive for influenza A+B, never/seldom exercise (as reference) was associated with 5.8% to 8.5% excess risks (ER) of mortality (P<0.0001), while low/moderate exercise was associated with ER which were 4.2% to 6.4% lower than those of the reference (P<0.001 for all-natural causes; P = 0.001 for cardiovascular; and P = 0.07 for respiratory mortality). Frequent exercise was not different from the reference (change in ER -0.8% to 1.7%, P = 0.30 to 0.73).
  
  
  CONCLUSIONS
  When compared with never or seldom exercise, exercising at low to moderate frequency is beneficial with lower influenza-associated mortality.
authors.affiliation: Department of Community Medicine, School of Public Health, The University of Hong Kong, Hong Kong, China.
authors.forename: Chit-Ming
authors.initials: CM
authors.lastname: Wong
authors.forename: Hak-Kan
authors.initials: HK
authors.lastname: Lai
authors.forename: Chun-Quan
authors.initials: CQ
authors.lastname: Ou
authors.forename: Sai-Yin
authors.initials: SY
authors.lastname: Ho
authors.forename: King-Pan
authors.initials: KP
authors.lastname: Chan
authors.forename: Thuan-Quoc
authors.initials: TQ
authors.lastname: Thach
authors.forename: Lin
authors.initials: L
authors.lastname: Yang
authors.forename: Yuen-Kwan
authors.initials: YK
authors.lastname: Chau
authors.forename: Tai-Hing
authors.initials: TH
authors.lastname: Lam
authors.forename: Anthony Johnson
authors.initials: AJ
authors.lastname: Hedley
authors.forename: Joseph Sriyal Malik
authors.initials: JS
authors.lastname: Peiris
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015897:Comorbidity; D015444:Exercise / Q000502:physiology*; D006801:Humans; D009980:Influenza A virus; D009981:Influenza B virus; D007251:Influenza, Human / Q000150:complications / Q000401:mortality / Q000628:therapy*; D008019:Life Style; D008875:Middle Aged; D016017:Odds Ratio; D016012:Poisson Distribution; D012044:Regression Analysis; D012307:Risk Factors; D016019:Survival Analysis