title: Carboxyhaemoglobin levels and their determinants in older British men.
abstract: BACKGROUND
  Although there has been concern about the levels of carbon monoxide exposure, particularly among older people, little is known about COHb levels and their determinants in the general population. We examined these issues in a study of older British men.
  
  
  METHODS
  Cross-sectional study of 4252 men aged 60-79 years selected from one socially representative general practice in each of 24 British towns and who attended for examination between 1998 and 2000. Blood samples were measured for COHb and information on social, household and individual factors assessed by questionnaire. Analyses were based on 3603 men measured in or close to (< 10 miles) their place of residence.
  
  
  RESULTS
  The COHb distribution was positively skewed. Geometric mean COHb level was 0.46% and the median 0.50%; 9.2% of men had a COHb level of 2.5% or more and 0.1% of subjects had a level of 7.5% or more. Factors which were independently related to mean COHb level included season (highest in autumn and winter), region (highest in Northern England), gas cooking (slight increase) and central heating (slight decrease) and active smoking, the strongest determinant. Mean COHb levels were more than ten times greater in men smoking more than 20 cigarettes a day (3.29%) compared with non-smokers (0.32%); almost all subjects with COHb levels of 2.5% and above were smokers (93%). Pipe and cigar smoking was associated with more modest increases in COHb level. Passive cigarette smoking exposure had no independent association with COHb after adjustment for other factors. Active smoking accounted for 41% of variance in COHb level and all factors together for 47%.
  
  
  CONCLUSIONS
  An appreciable proportion of men have COHb levels of 2.5% or more at which symptomatic effects may occur, though very high levels are uncommon. The results confirm that smoking (particularly cigarette smoking) is the dominant influence on COHb levels.
authors.affiliation: Division of Community Health Sciences, St George's, University of London, London SW17 0RE, UK. pwhincup@sgul.ac.uk
authors.forename: Peter
authors.initials: P
authors.lastname: Whincup
authors.forename: Olia
authors.initials: O
authors.lastname: Papacosta
authors.forename: Lucy
authors.initials: L
authors.lastname: Lennon
authors.forename: Andrew
authors.initials: A
authors.lastname: Haines
mesh_terms: D000368:Aged; D002249:Carbon Monoxide Poisoning / Q000097:blood / Q000209:etiology; D002263:Carboxyhemoglobin / Q000032:analysis*; D003430:Cross-Sectional Studies; D004305:Dose-Response Relationship, Drug; D005191:Family Characteristics; D005194:Family Practice; D006306:Health Surveys; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012111:Residence Characteristics; D012307:Risk Factors; D012621:Seasons; D012907:Smoking / Q000009:adverse effects / Q000097:blood*; D012959:Socioeconomic Factors; D011795:Surveys and Questionnaires; D013997:Time Factors; D006113:United Kingdom
chemical_list: D002263:Carboxyhemoglobin