Sleep as Medicine: Light, Meals, Warmth and Mind

A third of our lives

A third of our lives is spent asleep, and the recommended amount for most adults is 7–9 hours. Even so, the presentation reports a 30% drop in average sleep time over 40 years in the US (book data). Both short and poor-quality sleep contribute to chronic disease, which is why restorative sleep counts as one of the six pillars of lifestyle medicine.

The effect on appetite is striking: when sleep is cut short, leptin (a fullness signal) falls and ghrelin (a hunger signal) rises. After a single 4-hour night, 300–500 kcal of extra intake is seen, mostly carbohydrate. Nighttime cortisol rises and blood glucose can rise too; when impulse control is weaker, low-nutrient, large-portion foods become more tempting.

From the heart to mood, from night shifts to digestion

The first clues on cardiovascular health came from night-shift workers, who have more hypertension and coronary artery disease. Short sleep raises sympathetic (stimulating) nerve activity and vascular tone, and the normal nighttime dip in blood pressure can be blunted. Even a single short night can raise markers of inflammation and adhesion in the inner lining of blood vessels.

On mood, negative feelings, anxiety and stress reactivity rise. Cause and effect remain unclear, yet in prospective (forward-looking) studies sleep loss predicts later depression and anxiety, especially in adolescents. The inflammation markers interleukin-6 (IL-6) and C-reactive protein (CRP) may also rise; the presentation notes this could be a shared mechanism behind heart disease, type 2 diabetes, rheumatoid arthritis, multiple sclerosis (MS), cancer and depression.

Night shift work is associated with breast, prostate and colon cancer, and nighttime light exposure shows a suggestive link with breast cancer. DNA repair, much of which happens during sleep, can be disrupted. Digestion shows a similar picture. The microbiota follow the circadian rhythm, and shift work brings more complaints resembling irritable bowel syndrome (IBS) and indigestion. Nighttime reflux breaks sleep, and poor sleep lowers the threshold for feeling reflux.

The circadian rhythm: light and warmth

Circadian biology (the body’s 24-hour clock) offers a fitting scientific framework for sleep. In darkness, the brain’s pineal gland releases melatonin and sleepiness begins; even dim light such as screens can suppress it. Blue wavelengths (~480 nm) suppress it most strongly and warm white light (incandescent bulbs, candles) least. Meanwhile, indoor lighting is 100–1000 times weaker than the sunlight of even a cloudy day, and low light by day increases sensitivity to light at night.

The second key factor is body temperature. Core temperature is lowest during sleep and highest in the late afternoon, a difference of about 1 °C. To fall asleep the body must cool: skin vessels widen and release heat into the air, and this continues for roughly 4 hours after sleep onset. Warm hands and feet are a sign of falling asleep quickly. Stress, too little water, daytime inactivity and excess carbohydrate and salt before bed can disturb this heat loss.

Assessing sleep

Sleep assessment falls under three headings: duration, quality and regularity. For duration the aim is 7–9 hours, with under 6 and over 9 hours the riskiest ends. For quality the key question is whether sleep feels deep and refreshing; the trouble may be falling asleep, staying asleep or waking early. For regularity, bed and wake times and weekend differences matter. Telling apart voluntary from involuntary short sleep shapes the approach.

Chronic, marked daytime tiredness, especially with a high body mass index and hypertension, should raise the possibility of obstructive sleep apnea (repeated pauses in breathing during sleep). The STOP criteria are loud snoring, daytime tiredness, observed breathing pauses in sleep and high blood pressure. With two or more, a physician would suggest referral for sleep apnea evaluation. The presentation calls sleep a “vital sign” to ask about in every patient.

A sleep “prescription” with four factors

The presentation’s prescription rests on four factors. Light: switch off unneeded lights and screens 60–90 minutes before bed, and get 30–60 minutes of natural light in total during the day. Meals: have breakfast within 1 hour of waking, supplying at least 30% of daily calories; finish a light dinner at least 2–3 hours before bed. Warmth: let the bedroom cool gradually through the night, exercise in the afternoon or early evening, and avoid intense activity in the 60–90 minutes before bed.

The fourth factor is the mind. As the presentation reports, cognitive behavioral therapy for insomnia (CBT-I) and mindfulness meditation improve sleep quality; CBT-I is the first-line treatment for chronic insomnia (ACP: American College of Physicians, 2016; AASM: American Academy of Sleep Medicine, 2021). During nighttime wakefulness, following the breath is advised over planning. The prescription is tailored to whether the problem lies in falling asleep, staying asleep or waking. These measures do not replace a physician’s assessment and treatment but are added to them; if problems persist, consult your physician.