Holistic Health Factors That Affect Caffeine Sensitivity By Richard N. Fogoros, MD facebook linkedin Richard N. Fogoros, MD, is a retired professor of medicine and board-certified internal medicine physician and cardiologist. Learn about our editorial process Richard N. Fogoros, MD Medically reviewed by Medically reviewed by Arno Kroner, DAOM, LAc on March 20, 2021 facebook twitter linkedin Arno Kroner, DAOM, LAc, is a board-certified acupuncturist, herbalist, and integrative medicine doctor practicing in Santa Monica, California. Learn about our Medical Review Board Arno Kroner, DAOM, LAc on March 20, 2021 Print David Emmite / Getty Images Caffeine sensitivity refers to how much effect caffeine has on our bodies. When people who have unusually high caffeine ingest even a small amount of caffeine, they may experience significant symptoms, such as: Anxiety Tremors Headache Palpitations Insomnia If you have a high caffeine sensitivity, you should generally try to avoid caffeine altogether. How sensitive you are to caffeine is determined by several factors, including age and sex, but the biggest factor is genetic. Also, caffeine sensitivity is strongly modulated by the use of oral contraceptives (birth control pills) and by pregnancy. 5 Foods You Should Not Eat During Pregnancy How Caffeine Is Metabolized Caffeine is rapidly absorbed from the intestines into the bloodstream, and it readily crosses the blood-brain barrier into the brain. During pregnancy, it freely crosses the placenta. In your brain, caffeine binds to receptors for a neurotransmitter called adenosine, thus preventing adenosine from attaching to them. Because adenosine sends the brain messages that it's time to sleep, blocking adenosine receptors has the effect of producing wakefulness. Caffeine is metabolized in the liver by an enzyme called CYP1A2, which breaks it down into chemicals called theophylline, paraxanthine, and theobromine. It's then excreted by the kidneys into the urine. The half-life of caffeine is typically between 4 and 6 hours, which is typically how long caffeine affects people. Stimulants and Why They're Addictive What Affects Caffeine Sensitivity? Sensitivity to caffeine is largely determined by the activity of the CYP1A2 enzyme in the liver. The more active the CYP1A2, the less sensitive we are to caffeine. Several factors affect CYP1A2 activity. Age: CYP1A2 activity tends to decrease with age, so older people tend to be more sensitive to caffeine. Sex: Women tend to have lower CYP1A2 activity than men. Oral Contraceptive Use and Pregnancy: Estrogens inhibit CYP1A2 activity and caffeine sensitivity increases. Genetic Makeup: Several gene variants have now been identified that affect CYP1A2 activity. Your Genes and Caffeine Sensitivity Genetic testing has revealed three general categories of caffeine sensitivity related to our genetic makeup: Hypersensitivity to caffeine: These people have very low CYP1A2 activity. They have a strong response to even small amounts of caffeine, and will commonly experience jitters and insomnia. Normal sensitivity to caffeine: This is the vast majority of people. They can consume up to 400 mg of caffeine per day without adverse side effects. Low Sensitivity to Caffeine: These people have very high CYP1A2 activity, and often experience no effect at all from consuming caffeine. Smokers often have increased CYP1A2 activity. While genetic testing can categorize your level of caffeine sensitivity, having formal testing is generally not necessary for you to know—at least generally speaking—whether you're highly sensitive to caffeine. If you are, it's likely that nobody needs to tell you to cut back. Pregnancy and Caffeine Sensitivity Pregnancy reliably increases sensitivity to caffeine. The half-life of caffeine in pregnant women is often four times longer than it is for non-pregnant women—up to 16 hours. Furthermore, caffeine readily enters the bloodstream of the fetus, and the fetus has very, very little CYP1A2 activity. While serious adverse effects on the fetus caused by the mother’s caffeine intake have not been documented, this issue has not been studied extensively. In general, pregnant women are advised to limit or avoid caffeine. Was this page helpful? Thanks for your feedback! Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life. Sign Up You're in! Thank you, {{form.email}}, for signing up. There was an error. Please try again. What are your concerns? Other Inaccurate Hard to Understand Submit Article Sources Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. Mayo Clinic. Caffeine: how much is too much? 2017. Nehlig A. Interindividual Differences in Caffeine Metabolism and Factors Driving Caffeine Consumption. Pharmacol Rev. 2018;70(2):384-411. doi:10.1124/pr.117.014407 Elmenhorst D, Elmenhorst EM, Hennecke E, et al. Recovery sleep after extended wakefulness restores elevated A adenosine receptor availability in the human brain. Proc Natl Acad Sci USA. 2017;114(16):4243-4248. doi:10.1073/pnas.1614677114 U.S. National Library of Medicine. Caffeine. dePaula J, Farah A. Caffeine consumption through coffee: content in the beverage, metabolism, health benefits and risks. Beverages. 2019;5(37). doi:10.3390/beverages5020037 Rhee J, Kim R, Kim Y, et al. Maternal Caffeine Consumption during Pregnancy and Risk of Low Birth Weight: A Dose-Response Meta-Analysis of Observational Studies. PLoS ONE. 2015;10(7):e0132334. doi:10.1371/journal.pone.0132334 Additional Reading Cornelis MC, Byrne EM, Esko T, et al. The Coffee and Caffeine Genetics Consortium. Genome-wide meta-analysis identifies six novel loci associated with habitual coffee consumption. Molecular Psychiatry 20, 647-656 (May 2015) | doi:10.1038/mp.2014.107 Grant DM, Tang BK, Kalow W. Variability in caffeine metabolism. Clinical Pharmacology & Therapeutics, 33(5), 591-602, 1983. Grosso LM, Bracken MB. Caffeine metabolism, genetics, and perinatal outcomes: a review of exposure assessment considerations during pregnancy. Ann Epidemiol 2005; 15:460.