Introduced by David Spiegelhalter and Alejandro Leiva, microlives are intended as a simple way of communicating the impact of a lifestyle or environmental risk factor, based on the associated daily proportional effect on expected length of life. Similar to the micromort (one in a million probability of death) the microlife is intended for "rough but fair comparisons between the sizes of chronic risks". This is to avoid the biasing effects of describing risks in relative hazard ratios, converting them into somewhat tangible units. Similarly they bring long-term future risks into the here-and-now as a gain or loss of time.
- "A daily loss or gain of 30 minutes can be termed a microlife, because 1 000 000 half hours (57 years) roughly corresponds to a lifetime of adult exposure."
The microlife exploits that for small hazard ratios the change in life expectancy is roughly linear. They are by necessity rough estimates, based on averages over population and lifetime. Effects of individual variability, short-term or changing habits, and causal factors are not taken into account.
Microlives gained/lost, based on estimated life expectancy effects of long term lifestyle and demographic risk factors, for men and women aged 35 years. Risk factor Men Women Smoking Smoking 15–24 cigarettes −10 −9 Alcohol intake First drink (of 10 g alcohol) 1 1 Each subsequent drink (up to 6) −½ −1 Obesity Per 5 units above body mass index of 22.5 each day −3 −3 Per 5 kg above optimum weight for average height each day −1 −1 Sedentary behaviour 2 hours watching television −1 −1 Diet Red meat, 1 portion (85 g, 3 oz) −1 −1 Fruit and vegetable intake, =5 servings (blood vitamin C >50 nmol/L) 4 3 Coffee intake 2-3 cups 1 1 Physical activity First 20 minutes of moderate exercise 2 2 Subsequent 40 minutes of moderate exercise 1 ½ Statins Taking a statin 1 1 Air pollution Per day living in Mexico City v London −½ −½ Geography Per day being a resident of Russia v Sweden −21 −9 Era Per day living in 2010 v 1910 15 15 Per day living in 2010 v 1980 8 5
- David Spiegelhalter, Using speed of ageing and "microlives" to communicate the effects of lifetime habits and environment, BMJ, 345, December 2012, doi 10.1136/bmj.e8223 , as corrected by BMJ 2012;345:e8676 
- Haybittle JL. The use of the Gompertz function to relate changes in life expectancy to the standardized mortality ratio. Int J Epidemiol1998;27:885-9.