Does night screen use affect immunity?

Yes — even if total sleep duration is adequate, chronic late-night screen exposure can impair recovery and immune regulation. Blue light suppresses melatonin and shifts circadian timing, which subtly alters cortisol rhythm, growth hormone release, and nighttime parasympathetic activity — all critical for tissue repair and immune function. Beyond light itself, cognitive stimulation and emotional engagement from phone use can elevate sympathetic tone, reducing sleep depth and slow-wave quality even if you’re in bed long enough. Over time, it’s sleep quality and circadian alignment — not just hours slept — that determine recovery efficiency.