title: Outdoor temperature is associated with serum HDL and LDL.
abstract: BACKGROUND
  While exposures to high and low air temperatures are associated with cardiovascular mortality, the underlying mechanisms are poorly understood. The risk factors for cardiovascular disease include high levels of total cholesterol and low-density lipoprotein (LDL), and low levels of high-density lipoprotein (HDL). We investigated whether temperature was associated with changes in circulating lipid levels, and whether this might explain part of the association with increased cardiovascular events.
  
  
  METHODS
  The study cohort consisted of 478 men in the greater Boston area with a mean age of 74.2 years. They visited the clinic every 3-5 years between 1995 and 2008 for physical examination and to complete questionnaires. We excluded from analyses all men taking statin medication and all days with missing data, resulting in a total of 862 visits. Associations between three temperature variables (ambient, apparent, and dew point temperature) and serum lipid levels (total cholesterol, HDL, LDL, and triglycerides) were studied with linear mixed models that included possible confounders such as air pollution and a random intercept for each subject.
  
  
  RESULTS
  We found that HDL decreased -1.76% (95% CI: from -3.17 to -0.32, lag 2 days), and -5.58% (95% CI: from -8.87 to -2.16, moving average of 4 weeks) for each 5°C increase in mean ambient temperature. For the same increase in mean ambient temperature, LDL increased by 1.74% (95% CI: 0.07-3.44, lag 1 day) and 1.87% (95% CI: 0.14-3.63, lag 2 days). These results were also similar for apparent and dew point temperatures. No changes were found in total cholesterol or triglycerides in relation to temperature increase.
  
  
  CONCLUSIONS
  Changes in HDL and LDL levels associated with an increase in ambient temperature may be among the underlying mechanisms of temperature-related cardiovascular mortality.
authors.affiliation: Department of Environmental Health, Harvard School of Public Health, Landmark Center West room 415 E, 401 Park Drive, Boston, MA 02215, USA. jaana.halonen@ttl.fi
authors.forename: Jaana I
authors.initials: JI
authors.lastname: Halonen
authors.forename: Antonella
authors.initials: A
authors.lastname: Zanobetti
authors.forename: David
authors.initials: D
authors.lastname: Sparrow
authors.forename: Pantel S
authors.initials: PS
authors.lastname: Vokonas
authors.forename: Joel
authors.initials: J
authors.lastname: Schwartz
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000393:Air Pollutants / Q000032:analysis; D002318:Cardiovascular Diseases / Q000453:epidemiology / Q000209:etiology; D002784:Cholesterol / Q000097:blood; D015331:Cohort Studies; D004784:Environmental Monitoring; D062665:Epidemiological Monitoring; D006801:Humans; D006813:Humidity; D008075:Lipoproteins, HDL / Q000097:blood*; D008077:Lipoproteins, LDL / Q000097:blood*; D008297:Male; D008404:Massachusetts; D008875:Middle Aged; D010126:Ozone / Q000032:analysis; D052638:Particulate Matter / Q000032:analysis; D053260:Soot / Q000032:analysis; D013696:Temperature; D055815:Young Adult
chemical_list: D000393:Air Pollutants; D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL; D052638:Particulate Matter; D053260:Soot; D010126:Ozone; D002784:Cholesterol