Light exposure at night predicts incidence of cardiovascular diseases

Original Article ↗ Hacker News Discussion ↗

Study design, duration, and status

  • Participants wore wrist light trackers for one week; some argue this is too short, others say habits are stable enough and the very large sample (~88k) compensates.
  • The paper is a preprint and not yet peer reviewed; several commenters stress this should frame how seriously it’s taken, but others argue preprints are worth discussing and that peer review is an imperfect filter.
  • Conflict-of-interest disclosure (authors tied to a circadian-health company) raises skepticism for some; others note this also implies expertise and that their product (light sensors) limits the scope for big profit.

Correlation, causation, and confounders

  • The study reports correlations, not causation; commenters debate how far one can go in interpreting this.
  • It adjusts for many factors (activity, smoking, alcohol, diet, sleep duration, SES, polygenic risk), but people question:
    • Whether age and stress are adequately handled.
    • Whether air quality is still a major unmeasured confounder, since bright nights often mean polluted urban environments.
  • Shift work is a popular alternative explanation. The authors reportedly exclude shift workers and still see significant associations, though some remain unconvinced this fully removes the effect.

Possible mechanisms

  • Several note existing evidence that night light disrupts circadian rhythms and melatonin, and that the suprachiasmatic nucleus (SCN) affects hormones and metabolism, making a cardiovascular pathway plausible.
  • Others speculate that cardiovascular disease or insomnia could themselves increase nighttime light exposure (e.g., more wakefulness, windows open).

Effect sizes and subgroups

  • One commenter cites adjusted hazard ratios around 1.2–1.5 for various cardiovascular outcomes in the brightest-night group, with stronger associations in women and younger participants.
  • Some feel this “robust” pattern is compelling; others highlight remaining unmeasured factors.

Practical responses and personal anecdotes

  • People discuss how dark their bedrooms actually are: the “safer” group had 0–1.21 lux at night, surprising those used to city-light levels (10–20 lux).
  • Nighttime bathroom trips lead to suggestions: very dim/red/blue lights, nightlights, phone flashlights, or smart bulbs that dim to darkness.
  • Several describe needing light to fall asleep (linked by one to nyctophobia), and question what to do when personal comfort conflicts with population-level correlations.