Life expectancy for a healthy American man of my age is about 90. (That’s not to be confused with American male life expectancy at birth, only about 78.) If I’m to achieve my statistical quota of 15 more years of life, that means about 15 times 365, or 5,475, more showers. But if I were so careless that my risk of slipping in the shower each time were as high as 1 in 1,000, I’d die or become crippled about five times before reaching my life expectancy. I have to reduce my risk of shower accidents to much, much less than 1 in 5,475.

This calculation illustrates the biggest single lesson that I’ve learned from 50 years of field work on the island of New Guinea: the importance of being attentive to hazards that carry a low risk each time but are encountered frequently.

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Consider: If you’re a New Guinean living in the forest, and if you adopt the bad habit of sleeping under dead trees whose odds of falling on you that particular night are only 1 in 1,000, you’ll be dead within a few years. In fact, my wife was nearly killed by a falling tree last year, and I’ve survived numerous nearly fatal situations in New Guinea.

I now think of New Guineans’ hypervigilant attitude toward repeated low risks as “constructive paranoia”: a seeming paranoia that actually makes good sense. Now that I’ve adopted that attitude, it exasperates many of my American and European friends. But three of them who practice constructive paranoia themselves — a pilot of small planes, a river-raft guide and a London bobby who patrols the streets unarmed — learned the attitude, as I did, by witnessing the deaths of careless people.

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Having learned both from those studies and from my New Guinea friends, I’ve become as constructively paranoid about showers, stepladders, staircases and wet or uneven sidewalks as my New Guinea friends are about dead trees. As I drive, I remain alert to my own possible mistakes (especially at night), and to what incautious other drivers might do.

My hypervigilance doesn’t paralyze me or limit my life: I don’t skip my daily shower, I keep driving, and I keep going back to New Guinea. I enjoy all those dangerous things. But I try to think constantly like a New Guinean, and to keep the risks of accidents far below 1 in 1,000 each time.

If the risk of dying by falling in the shower is only 1 in a 1,000, then a shower would kill someone in just a few years. We concern ourselves with risks that are out of our control, but we should be vigilantly mindful of the mundane daily risks we take on a regular basis, like driving our cars, standing on a stepladder, or taking a shower.

Methods: A population sample of 4,512 (1,945 men) Scottish Health Survey 2003 respondents (35 years) were followed up to 2007 for all-cause mortality and CVD events (fatal and nonfatal combined). Main exposures were interviewer-assessed screen time (<2 h/day; 2 to <4 h/day; and 4 h/day) and moderate to vigorous intensity physical activity.

Results: Two hundred fifteen CVD events and 325 any-cause deaths occurred during 19,364 follow-up person-years. The covariable (age, sex, ethnicity, obesity, smoking, social class, long-standing illness, marital status, diabetes, hypertension)-adjusted hazard ratio (HR) for all-cause mortality was 1.52 (95% confidence interval [CI]: 1.06 to 2.16) and for CVD events was 2.30 (95% CI: 1.33 to 3.96) for participants engaging in 4 h/day of screen time relative to <2 h/day. Adjusting for physical activity attenuated these associations only slightly (all-cause mortality: HR: 1.48, 95% CI: 1.04 to 2.13; CVD events: HR: 2.25, 95% CI: 1.30 to 3.89). Exclusion of participants with CVD events in the first 2 years of follow-up and previous cancer registrations did not change these results appreciably. Approximately 25% of the association between screen time and CVD events was explained collectively by C-reactive protein, body mass index, and high-density lipoprotein cholesterol.

Conclusions: Recreational sitting, as reflected by television/screen viewing time, is related to raised mortality and CVD risk regardless of physical activity participation. Inflammatory and metabolic risk factors partly explain this relationship.

The longer you sit, the greater your chances of death.