Caffeine Toxicity and Nerve Damage By Sirah Dubois Caffeine is the most widely consumed and unregulated stimulant in the world. The majority of Americans knowingly or unknowingly consume caffeine each day, usually from coffee, tea and soda, but also from chocolate, energy drinks and many over-the-counter medications. In the quantities found in most food and drinks, caffeine is very unlikely to cause toxicity; however, many drugs contain high levels of caffeine and pose a considerable risk for some users. Nerve damage can develop as a consequence of excessive caffeine intake, but it is not the most common symptom. Prevalence of Caffeine Toxicity According to "Nutrition Concepts & Controversies," 3,343 cases of caffeine poisoning were reported to the American Association of Poison Control Center in 2009. Of the 3,343 cases, 1,249 represented children younger than 6 years old, mainly because of their smaller size and lesser ability to metabolize caffeine and remove it from their blood serum. Death is not an uncommon result of caffeine toxicity, with the causes often related to heart failure, seizures and adrenal failure. There is no data to suggest that race or gender alter the biochemical effects of caffeine. Video of the Day Unsafe Dosages In adults, lethal toxicity from caffeine is estimated to occur between 150 and 200 mg/kg, which equates to drinking at least 80 cups of brewed coffee in a short period of time, according to the "Complete Guide to Prescription and Non-prescription Drugs" by H. Winter Griffith, M.D. In terms of lethal dosages, consumption of between 7 and 10 g of caffeine will kill most adults. Caffeine doses of 78 mg/kg can cause toxicity and serious adverse effects in young children. In 1989, the US Food and Drug Administration limited the amount of caffeine in over-the-counter drugs to a maximum of 200 mg/dose. Caffeine is commonly found in alertness-promoting drugs, menstrual aids, pain killers and diet aids. Toxicity Symptoms Caffeine affects your central nervous system, heart, blood vessels, adrenal glands, thyroid gland, kidneys and a variety of neurotransmitters and hormones, but it is dose dependent. For example, at doses between 85 and 250 mg, caffeine may cause feelings of alertness, reduced fatigue and eased flow of thought, according to "Functional Biochemistry in Health and Disease." Doses between 250 and 500 mg can cause undesirable effects, such as restlessness, nervousness, insomnia, fatigue and tremors. Higher daily doses can cause severe glandular fatigue from over-production of adrenaline and other hormones, cardiovascular problems and altered brain activity that culminates in seizures. People most at risk for severe caffeine toxicity are bodybuilders and other athletes that intentionally supplement with caffeine, people addicted to drugs with caffeine, long-term energy drink addicts and epileptics, as noted by Sari Edelstein, author of "Nutrition and Public Health." Caffeine and Nerve Damage Caffeine can damage nerves in a couple of ways. According to the book "Advanced Nutrition and Human Metabolism," the main action of caffeine is to counteract the effects of the brain chemical adenosine, which results in reduced blood flow to your brain and damage to neurons. Damage to neurons in your brain is experienced as headaches, dizziness, seizures and reduced fine-motor coordination in your hands. Further, caffeine indirectly promotes the depletion of B vitamins, some of which are needed for conductance and maintenance of nerves. As such, high consumption of caffeine can cause numbness and tingling in your arms, legs and around your head. Reducing your caffeine consumption and supplementing with a B-complex vitamin should help combat these symptoms. Long-term vitamin B-6 and B-12 deficiency often results in permanent nerve damage. Can drinking coffee make you go blind? Monday 8 October 2012 Switching to decaf could save your sight, claims the Daily Mail. The newspaper reports that drinking three or more cups of coffee a day is linked with vision loss and blindness. The story is based on a study that looked at the association between caffeine consumption and exfoliation glaucoma. Exfoliation glaucoma is a condition in which fluid builds up inside the eye, putting pressure on the optic nerve. This leads to a degree of sight loss and, in serious cases, total blindness. In the study, researchers compared rates of exfoliation glaucoma with drinking habits, focusing on caffeinated drinks such as coffee, tea and cola. The study found that drinking three or more cups of caffeinated coffee daily was linked with increased risk of developing exfoliation glaucoma. Curiously, a similar increase was not found with other caffeinated products. This was a large, well-conducted study, but it does not directly or conclusively show that caffeinated coffee causes vision loss. This is because it relied on people recalling their coffee intake over long periods and involved relatively few people with the condition. By far the greatest risk of exfoliation glaucoma was among those with a family history of glaucoma – which is a factor already known to be linked with developing glaucoma. Coffee has been linked in the past with both health problems and health benefits. So, despite the headlines, there’s no need to ditch the cappuccino altogether, but it makes sense to drink coffee and other caffeinated products in moderation. Where did the story come from? The study was carried out by researchers from Brigham and Women's Hospital, Harvard Medical School and other US institutions. It was funded by the National Institutes of Health and other academic institutions. The study was published in the peer-reviewed journal Investigative Ophthalmology and Visual Science. The Mail’s headline was unnecessarily alarmist. Its claim that switching to decaf could save your sight exaggerated the results of the study and is likely to be wrong because of the link between glaucoma and family history. What kind of research was this? The researchers drew on two large prospective cohort studies to look at the association between caffeine and exfoliation glaucoma. While useful, cohort studies cannot prove cause and effect on their own. To do this other types of evidence are needed. It is always possible that other factors, such as diet and family history, might influence people’s health outcomes. These are called confounders. Although, the best cohort studies try to take these into account. The researchers point out that exfoliation glaucoma is a leading cause of secondary angle glaucoma worldwide. Secondary glaucoma is when a secondary factor, such as injury or infection blocks the drainage tubes inside the eyes. As a result, ‘intraocular’ pressure builds up and this can damage the optic nerve and the nerve fibres. In cases of exfoliation glaucoma, the secondary factor is the build-up of abnormal deposits of cells, known as exfoliation deposits, inside the eye. These have been described as the “optical version of dandruff”. This can lead to: deposits building up on the lens of the eye, causing an increase in intraocular pressure damage to the optic nerve or retina narrowing of the visual field, which causes a form of tunnel vision This process is known as exfoliation syndrome (ES). If all three changes are present, a person is diagnosed with exfoliation glaucoma. If only one of the changes happens then a patient will have 'exfoliation glaucoma suspect' (EGS). The researchers say exfoliation glaucoma and ES and the changes that typify it have been found to occur at high levels in Scandinavia, where coffee consumption is also high. They also say that coffee is associated with increased levels of a substance called homocysteine in blood, aqueous humour and tear fluid, and that this may help trigger or accelerate the development of exfoliation deposits. They say that this means caffeine or coffee consumption is “an attractive risk factor” for ES and exfoliation glaucoma. What did the research involve? The researchers followed two large groups of people: 78,977 women from a large US study called the Nurses Health Study (NHS), which began in 1980 41,202 men from the Health Professionals Follow-up Study (HPFS), which began in 1986 Both studies continued until 2008 and, in each, participants were asked every two years to fill in detailed questionnaires covering their health, lifestyle and diets. For this particular piece of research, participants had to be at least 40 years old and had to have not reported glaucoma at the start of the study. They also had to report regular eye examinations. During the study period, researchers used a validated food frequency questionnaire to collect information from participants on their dietary intake. For those in the NHS, this was conducted every two years from 1980 to 1986 and every four years after, and for men in the HPFS this was conducted in 1986 and every four years after. Participants were questioned about consumption of caffeinated coffee (in cups), caffeinated tea (in cups) and caffeinated chocolate (in 1oz servings). Later, this was expanded to include intake of decaffeinated coffee (in cups), and caffeinated and caffeine-free sodas. For all these items the questionnaire allowed for nine responses for the frequency of intake, ranging from “Never, or less than once a month” to “Six or more times a day”. Answers were converted into average daily intake of caffeine in mg/day. The researchers assumed 137mg of caffeine per cup of coffee, with far lower amounts of caffeine assumed for tea, cola and chocolate. During the study period, the researchers collected self-reported information about the development of glaucoma. They then asked for additional detailed information in the form of a glaucoma questionnaire from the participants’ eye care providers. This included questions on the presence of exfoliation deposits. A glaucoma specialist evaluated the returned questionnaires. For their analysis, the researchers defined exfoliation glaucoma or EGS as the presence of documented exfoliation syndrome plus other signs of exfoliation deposits in the eye. They analysed the association between caffeine and caffeinated drinks consumption and the risk of exfoliation glaucoma or EGS, using standard statistical methods. Since glaucoma is a slowly developing chronic condition, they say they calculated the cumulative caffeine intake, averaging the intake from all the dietary assessments made. The researchers adjusted the results to account for various other risk factors for glaucoma, including: family history history of heart attack body mass index smoking What were the basic results? The researchers found that, compared with people who drank no caffeinated coffee, those who drank three or more cups of caffeinated coffee daily were at increased risk of exfoliation glaucoma or EGS (risk ratio 1.66, 95% confidence interval 1.09 to 2.54). These results were not significantly altered after adjustment for total fluid intake. Associations were stronger among women with a family history of glaucoma. In terms of lower levels of caffeinated coffee consumption they found that, compared with participants whose coffee consumption was less than 125mg/day, in those who consumed 500mg or more of coffee a day there was a trend towards increased risk of exfoliation glaucoma or EGS. However, the increase was not statistically significant (risk ratio 1.43, 95% confidence interval 0.98 to 2.08). This means the trend could have occurred by chance. Researchers did not find associations with consumption of other caffeinated products (caffeinated soda, caffeinated tea or chocolate) or decaffeinated coffee and the risk of exfoliation glaucoma or EGS. How did the researchers interpret the results? The researchers say that their study supports the hypothesis that three or more cups of caffeinated coffee daily may contribute to the gradual accumulation of exfoliation material in the eye. They point out that the previous findings that coffee consumption elevates homocysteine levels provides a plausible biological link between coffee consumption and exfoliation syndrome. Conclusion This was a large study that followed people for many years to assess the association between coffee and exfoliation glaucoma, using validated detailed questionnaires on dietary intake. However, it had several limitations, which could affect the reliability of its results: The researchers had to rely on information on non-standardised eye examinations from various eye care providers, to ascertain whether participants had exfoliation glaucoma or EGS, rather than having confirmed diagnoses. The fact that so few people were identified may mean that the participants did not recall their diagnoses accurately, something that would have reduced the study’s ability to detect a link. The researchers had to rely on people accurately recalling their intake of caffeine over the previous year. Their study populations were 90% caucasian, so the results may not apply to other ethnic groups. People of African or African-Caribbean origin are at increased risk of developing other types of glaucoma. Other factors called confounders may have affected the risk of people getting exfoliation glaucoma, although the researchers tried to take these into account.