Glossary

Terms you will meet in our articles, explained in plain English.

Allostatic load

The "price" the body pays for long-lasting or repeated activation of the stress systems; cumulative wear and tear linked to disease. Learn more →

Association vs. causation

When two things occur together (association), it does not mean one causes the other. Randomized controlled trials are the best way to test causation.

Body mass index (BMI)

Weight in kilograms divided by height in meters squared (or weight in pounds × 703 ÷ height in inches squared). A rough measure that does not account for body composition.

Cardiorespiratory fitness

The ability of the heart, lungs and muscles to sustain physical effort; a strong predictor of health and longevity. Learn more →

Case-control study

A study that compares people with a disease (cases) and without it (controls) to find factors linked to the disease.

CBT-I (cognitive behavioral therapy for insomnia)

The recommended first-line treatment for chronic insomnia, combining sleep restriction, stimulus control, cognitive techniques and sleep hygiene. Learn more →

Circadian rhythm

The body’s internal roughly 24-hour clock that regulates sleep, hormones and body temperature, set mainly by light. Learn more →

Clinical guideline

Recommendations from expert bodies such as the WHO, USPSTF or professional societies, based on a systematic review of the evidence.

Cognitive behavioral therapy (CBT)

A structured, evidence-based form of psychotherapy that works on the links between thoughts, emotions and behavior. Learn more →

Cohort study

A study that follows a group of people over time to see how habits or exposures relate to later health outcomes.

Confounder

A third factor that affects both a habit and an outcome, creating a false impression that they are linked.

Cortisol

A stress hormone released by the adrenal glands. It mobilizes energy in the short term; chronically high levels are linked to health problems.

Dietary fiber

The part of plant foods the body cannot digest. It supports gut health and fullness and is linked to lower risk of chronic disease. Learn more →

DOI (Digital Object Identifier)

A permanent digital identifier for a scientific publication. You can look up any article at doi.org. Learn more →

FASD (fetal alcohol spectrum disorders)

Lifelong conditions caused by alcohol exposure before birth, affecting growth, learning and behavior. Completely preventable. Learn more →

Ghrelin

A hormone that stimulates hunger. Its levels rise with sleep deprivation. Learn more →

Gut microbiome

The trillions of bacteria and other microbes living in the intestines, which influence digestion, immunity and metabolism. Learn more →

HDL cholesterol

"Good" cholesterol, which helps remove cholesterol from the bloodstream.

Heart rate variability (HRV)

The natural variation in time between heartbeats. Higher HRV is generally linked to better recovery and stress resilience. Learn more →

Hippocampus

A brain region important for memory. Aerobic exercise can increase its volume. Learn more →

LDL cholesterol

"Bad" cholesterol. High levels contribute to plaque in the arteries and heart disease.

Leptin

A hormone that signals fullness. Its levels drop with sleep deprivation. Learn more →

Level of evidence

How confident we can be in a conclusion, based on the type and quality of studies. Learn more →

Lifestyle medicine

An evidence-based branch of medicine that uses changes in daily habits to prevent and help treat chronic disease. Built on six pillars. Learn more →

MBSR (Mindfulness-Based Stress Reduction)

An 8-week group mindfulness program developed by Jon Kabat-Zinn at the University of Massachusetts in 1979. Learn more →

Melatonin

A hormone released in the evening darkness that signals the body it is time to sleep. Sold as a dietary supplement in the U.S. Learn more →

MET (metabolic equivalent)

A unit of the energy cost of an activity relative to resting. Moderate activity is about 3 to 6 METs; vigorous activity is more than 6.

Meta-analysis

A statistical method that combines the results of several studies to obtain a more precise overall estimate.

Mindfulness

The skill of paying attention to the present moment on purpose and without judgment. Learn more →

Nicotine replacement therapy (NRT)

Patches, gum, lozenges, inhalers and sprays that deliver nicotine without smoke to ease withdrawal while quitting. Learn more →

NOVA classification

A system that groups foods by degree of processing, from unprocessed to ultra-processed. Learn more →

NSAIDs

Nonsteroidal anti-inflammatory drugs such as ibuprofen, naproxen and diclofenac. Effective for pain but with risks for the heart, stomach and kidneys. Learn more →

Obstructive sleep apnea

Repeated pauses in breathing during sleep caused by the airway narrowing or closing; linked to high blood pressure and daytime sleepiness. Learn more →

Prediabetes

Blood sugar levels higher than normal but not yet in the diabetes range. About 1 in 3 U.S. adults has it; lifestyle change can prevent progression. Learn more →

Randomized controlled trial (RCT)

A study in which participants are randomly assigned to an intervention or a control group; the best design for testing cause and effect.

Relative risk

How much more or less likely an outcome is in one group compared with another. A 20% lower relative risk does not mean 20 out of 100 people are protected.

REM sleep

Rapid eye movement sleep, when most vivid dreaming occurs; important for emotional memory and skills. Learn more →

Rumination

Repetitive, negative thinking about problems or feelings; linked to depression and anxiety. Learn more →

Slow-wave (deep) sleep

The deepest stage of non-REM sleep, important for physical recovery and memory consolidation; it decreases with age. Learn more →

Social jet lag

The difference in sleep timing between workdays and days off, which throws off the body clock. Learn more →

Standard drink

In the U.S., a drink containing 14 g of pure alcohol: 12 oz of regular beer, 5 oz of wine or 1.5 oz of 80-proof spirits. Learn more →

Systematic review

A review that uses a predefined, transparent method to find, select and evaluate all relevant studies on a question.

Trans fats

Fats formed by partially hydrogenating vegetable oils. They raise LDL and lower HDL cholesterol; the FDA removed them from the U.S. food supply. Learn more →

Ultra-processed foods

Industrial products made mostly from substances extracted from foods or synthesized, such as soda, chips, hot dogs and packaged sweets. Learn more →