Clarifying life lost due to cold and heat: a new approach using annual time series.

Objective: To clarify whether deaths associated with hot and cold days are among the frail who would have died anyway in the next few weeks or months. Design: Time series regression analysis of annual deaths in relation to annual summaries of cold and heat. Setting: London, UK. Participants: 3 530 280 deaths from all natural causes among London residents between October 1949 and September 2006. Main outcome measures: Change in annual risk of death (all natural cause, cardiovascular and respiratory) associated with each additional 1°C of average cold (or heat) below (above) the threshold (18°C) across each year. Results: Cold years were associated with increased deaths from all causes. For each additional 1° of cold across the year, all-cause mortality increased by 2.3% (95% CI 0.7% to 3.8%), after adjustment for influenza and secular trends. The estimated association between hot years and all-cause mortality was very imprecise and thus inconclusive (effect estimate 1.7%, −2.9% to 6.5%)....