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Can drinking coffee cause glaucoma, colorectal cancer?

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Coffee. Photo: Medical News Today


• ‘There is need to conduct additional research on possible role of caffeine in causing colon cancer’
•Coffee’s association with glaucoma was seen in heavy consumers, those with highest genetic risk
•Experts recommend drinking no more than three or four cups per day to prevent chronic diseases

The media and the scientific community have been awash with reports associating heavy consumption of ‘hot’ coffee with glaucoma and colorectal cancer.

The studies have raised concerns among regular coffee drinkers. The confusion comes from earlier studies that demonstrated that drinking coffee helps to prevent liver damage, several cancers, type 2 diabetes and other chronic diseases.

So, can drinking coffee cause glaucoma and colorectal cancer?
A physician and President, National Association of Resident Doctors (NARD), Dr. Okhuaihesuyi Uyilawa, told The Guardian: “Coffee is extracted from coffee bean, Coffea arabica. The seeds of botanical genus Coffea may be raw, roasted, whole, or ground. The prepared drink through such coffee seeds is also called coffee. The main constituents of coffee are caffeine, tannin, fixed oil, carbohydrates, and proteins. It contains two–three per cent caffeine, three–five per cent tannins, 13 per cent proteins, and 10–15 per cent fixed oils. In the seeds, caffeine is present as a salt of chlorogenic acid (CGA). Also it contains oil and wax.”

Uyilawa said coffee is often used as antioxidants, but more importantly coffee is a good source of chromium and magnesium. On coffee and colorectal cancer, he said: “Coffee contains several bioactive compounds relevant to colon physiology. Also, coffee intake is a proposed protective factor for colorectal cancer (CRC), but current evidence still remains inconclusive.

Hot food generally including hot boluses of food, not just hot coffee, is a risk factor for colorectal cancer.”

On coffee and glaucoma, Uyilawa said the risk of developing glaucoma is raised by intraocular pressure (IOP), the pressure within the eyes, that is eye hypertension. “People who drink a lot of coffee do not seem to have a greater chance of having glaucoma, unless they already have a genetic risk of having high intraocular pressure or they already have glaucoma. This is because caffeine consumption may pose a greater risk in those with a genetic predisposition for a higher IOP. It has been shown in some recent research that there is no causal effect between coffee drinking and IOP,” the medical doctor said.

However, a chemist and Director of Lumos Laboratories, Abuja, Ejikeme Nwosu, disagrees. He told The Guardian: “High pressure in the eye is one of the causes of glaucoma. Lack of sleep is one of the causes of glaucoma. High consumption of coffee causes heightened alertness and lack of sleep, which builds up pressure in the eyes over time.

“So, with this simple plausible logic, it is very evident that high consumption of coffee can cause glaucoma.” Nwosu, who owns a patent in a technology that converts urine and other wastes into clean and renewable energy, added: “I could make faster comments on glaucoma and coffee because I was a heavy coffee consumer and suffered heightened eye pressures plus migraine.”

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A clinical pharmacist and National Chairman, Association of Hospital and Administrative Pharmacists of Nigeria (AHAPN), Dr. Kingsley Chiedu Amibor, told The Guardian: “Caffeine is one of the major components of coffee. Many people across the world drink coffee regularly. Coffee contains acrylamide, a potential carcinogen. However, recent studies into dietary acrylamide intake have found no association with cancer risk.

“Various research findings have shown no link between caffeine consumption and cancer. In some instances, higher coffee consumption has been associated with decreased incidence of colorectal cancer.

“A review of over 1,000 studies stated that there was no conclusive evidence to classify coffee as carcinogenic. Many studies indicated no effect of coffee consumption on the development of pancreatic, prostate, and breast cancers.

“Most of the accumulated evidence for colorectal cancer indicates that higher daily coffee consumption is associated with reduced incidence of colorectal cancer. A very recent meta-analysis of the association between coffee consumption and colorectal cancer showed that high coffee consumption was associated with a significantly reduced risk of colorectal cancer.”

Amibor said a combination of 16 cohort studies showed that high coffee consumption resulted in a slight reduction in the risk of colorectal cancer. He added: “Most of the recent research has indicated that coffee isn’t associated with an increased risk of cancer. In fact, drinking coffee is often associated with health benefits.”

However, the clinical pharmacist said a study carried out to examine the relationship of coffee intake to colorectal cancer incidence in a large observational cohort of postmenopausal women numbering over 700 suggested that increased incidence of colorectal cancer was associated with higher coffee consumption. “This result agrees with a number of other studies showing that coffee increases risk or has no effect,” he said.

Amibor further explained: “A large review of studies published in 2017 assessed coffee consumption and various health outcomes. It found no significant association between drinking coffee and several cancers, including colorectal, pancreatic and breast cancer.”

The hospital pharmacist said what all these reveal is the need to conduct additional research on the possible role of caffeine in causing colon cancer. “We can conclude by stating that it is okay to continue drinking the usual morning cup of coffee, however, modesty is required. It is not advisable to drink too much. Some health institutions like The Academy of Nutrition and Dietetics recommends drinking no more than three or four cups per day, and I equally advocate same,” Amibor said.

On coffee’s association with glaucoma, Amibor said: “A new study has found that consuming large amounts of daily caffeine may increase the risk of glaucoma more than three-fold for those genetically predisposed to higher eye pressure.

“The study results may suggest that patients with a strong family history of glaucoma should reduce their caffeine intake. This study is important because glaucoma is the second leading cause of blindness in Nigeria after cataract. The study looked at the impact of caffeine intake on glaucoma, and intraocular pressure, which is pressure inside the eye.

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“Elevated intraocular pressure is an integral risk factor for glaucoma, though other factors do contribute to this condition. With glaucoma, patients typically experience few or no symptoms until the disease progresses and they experience loss of vision.

“Some previous studies suggest that high caffeine intake increased the risk of the high-tension open angle glaucoma among people with a family history of the disease.

It is worth mentioning that the link between caffeine and glaucoma risk was only seen with a large amount of caffeine and in those with the highest genetic risk.”

The clinical pharmacist said some studies do not show that coffee causes glaucoma, but do suggest that drinking three or more cups of caffeinated coffee might not be good for the eyes.

He said a group of scientists applied caffeine eye drops directly on to healthy eyes, but they did not record any increase in eye pressure, suggesting that caffeine doesn’t appear to have a direct effect.

“For those who are at higher risk for glaucoma or have been diagnosed, there is need for them to have regular comprehensive dilated eye examinations and to use medications as directed,” Amibor said.

A consultant pharmacist and medical director of Merit Healthcare, Dr. Lolu Ojo, told The Guardian: “There are studies which tend to link daily coffee drinking with increased risk of glaucoma progression. Caffeine, a major component of coffee, causes intraocular pressure to rise.

“It has also been linked to increased production of a type eye fluid called aqueous humour. As the eye fluid volume rises, so does the pressure inside the eyes. There are other opinions that say that there is no evidence that the increase in intraocular caused by caffeine is clinically significant.

“Therefore, we cannot conclude that Coffee drinking causes glaucoma. However, it should be advised that glaucoma patients should minimise or avoid coffee intake.”

Meanwhile, several studies have shown that coffee is one of the most widely consumed beverages in the world. It contains many potentially bioactive components that are relevant to colon physiology including polyphenols (mainly chlorogenic acids), melanoidins, diterpenes, and caffeine, among others.

Although the levels of these compounds vary by species of coffee bean, degree of roasting, brewing technique, and serving size, scientists suggests that exposure to one or more of them may promote colon health via anti-mutagenic or antioxidant properties, reduction of bile acid secretion, modification of microbiome composition, and/or enhancement of critical bowel functions (example motility, stool output).

Also, according to the latest study on coffee and glaucoma, consuming large amounts of daily caffeine may increase the risk of glaucoma more than three-fold for those with a genetic predisposition to higher eye pressure.

The Icahn School of Medicine at Mount Sinai, New York, United States led the international, multi-centre study. It is the first to demonstrate a dietary – genetic interaction in glaucoma.

The study results published in the June print issue of Ophthalmology may suggest patients with a strong family history of glaucoma should cut down on caffeine intake.

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The study is important because glaucoma is the leading cause of blindness. It looks at the impact of caffeine intake on glaucoma, and intraocular pressure (IOP), which is pressure inside the eye. Elevated IOP is an integral risk factor for glaucoma, although other factors do contribute to this condition. With glaucoma, patients typically experience few or no symptoms until the disease progresses and they have vision loss.

The researchers studied dietary, health and genetic data on more than 120,000 adults aged from 39–73.
The findings, the team said, suggest that individuals with a strong family history of glaucoma would be best to cut down on their daily caffeine intake.

We previously published work suggesting that high caffeine intake increased the risk of the high-tension open angle glaucoma among people with a family history of disease,’ said

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The UK Biobank, a large-scale database containing detailed genetic and health information on half-a-million participants, collected data for the study.

Each participant was polled repeatedly about his or her diet — with a focus on how many caffeinated beverages they drank and how much caffeine-bearing food they consumed on a daily basis.

They were also asked questions about their vision — including whether they had glaucoma or if they had a family history of the condition — and, three years into the study, each subject had an eye examination including intraocular pressure checks.

The team first looked for relationships between caffeine intake, intraocular pressure and self-reported glaucoma, before assessing whether the genetic data altered these relationships.

The researchers found that, generally speaking, a high caffeine intake was not associated with an increased risk of intraocular pressure.

The exception was those with the strongest genetic predisposition to elevated IOP, that is those in the 75th percentile. For these subjects, greater caffeine consumption was associated with a higher intraocular pressure and prevalence of glaucoma.

Specifically, those who consumed the most caffeine daily — more than 480 milligrammes, which is roughly four cups of coffee — had intraocular pressures that were 0.35 mmHg higher than their peers.

And those with the highest level of genetic risk who consumed more than 321 mg of caffeine (around three cups of coffee) daily had a 3.9 fold higher glaucoma rates than their peers who had minimal caffeine or were at the lowest genetic risk.

Glaucoma is a condition, which can affect sight, usually due to build up of pressure within the eye. It often affects both eyes, usually to varying degrees. One eye may develop glaucoma quicker than the other. The eyeball contains a fluid called Aqueous Humour, which is constantly produced by the eye, with any excess drained though tubes.

Glaucoma develops when the fluid cannot drain properly and pressure builds up, known as the intraocular pressure. This can damage the optic nerve (which connects the eye to the brain) and the nerve fibres from the retina (the light-sensitive nerve tissue that lines the back of the eye).

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Glaucoma can be treated with eye drops, laser treatment or surgery. But early diagnosis is important because any damage to the eyes cannot be reversed. Treatment aims to control the condition and minimise future damage.

If left untreated, glaucoma can cause visual impairment. But if it’s diagnosed and treated early enough, further damage to vision can be prevented.

Indeed, coffee and cancer have had a rocky relationship over the years. Coffee was once recklessly touted as a cancer treatment and later declared a carcinogen. Today, new studies indicate it may help prevent certain types of cancer. And recently, a California judge stirred controversy by ruling that a health warning should be attached to coffee sold in that state.

Can coffee increase the risk of cancer? Chief of the Division of Outpatient Medicine at Cancer Treatment Centers of America and an Internist at our Philadelphia hospital, Dr. Anthony Perre, said: “There is no clear evidence linking coffee consumption and increased risk of cancer.”

In fact, the World Health Organisation (WHO) removed coffee from its list of carcinogens in 2016. WHO added coffee to its list of risk factors more than 25 years ago, but reversed course after more recent studies found no evidence that coffee increased cancer risk.

“A study published in 2017 showed that drinking two cups of coffee a day may lower the risk for several cancer types, including breast cancer, colorectal cancer, liver cancer and head and neck cancers,” Perre said. “There are probably a number of factors that may contribute to the reduced risk.” The bottom line is there’s no overwhelming evidence that coffee can cause or help prevent cancer.

Why is coffee considered a carcinogen in California? While there is no evidence coffee itself raises cancer risk, a substance formed when coffee is processed may. “There has been some concern about acrylamide, which is formed when coffee beans are roasted,” Perre said. In a court decision that stirred much debate, a California judge ruled that coffee sold in the state required a cancer warning because of the presence of acrylamide. The substance is listed among 900 chemicals that require warning labels under the state’s Safe Drinking Water and Toxic Enforcement Act, known as Prop 65. Acrylamide is a chemical used in the production of some paper and plastic products. It also forms in some starchy foods cooked at high temperatures. According to the American Cancer Society (ACS), “most of the studies done so far have not found an increased risk of cancer in humans.” But the ACS suggests more studies are needed. “For now, it is suggested that we may wish to reduce our consumption of other foods high in acrylamide—like French fries, potato chips, crackers, bread, cookies and breakfast cereals,” Perre said.

Can drinking hot coffee or other beverages increase cancer risk? In 2016, WHO classified hot beverages as a probable carcinogen after the International Agency for Research on Cancer concluded that very hot beverages could cause cell damage and inflammation that may lead to cancer. Experts recommend not drinking hot beverages above 149 degrees Fahrenheit, or 65 degrees Celsius.

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Are coffee enemas a viable treatment for colon cancer? Information abounds on the alleged cancer-treating benefits of coffee enemas. The theory behind this unusual treatment is that coffee delivered directly into the colon causes rapid caffeine absorption that jumpstarts detoxification. The treatment was part of The Gerson Therapy, named for Dr. Max Gerson, who promoted detoxification through enemas, juices and organic fruits and vegetables. In 1947, the National Cancer Institute called Gerson’s practice into question and found that cancer had progressed in all his patients. The U.S. Food and Drug Administration has not approved The Gerson Therapy to treat cancer or other diseases, and there is no evidence coffee enemas can successfully treat cancer. On the other hand, coffee enemas do come with some risks, including internal burns, colitis and infections.

Another study published in Journal of Epidemiology and titled “Tea, Coffee, and Milk Consumption and Colorectal Cancer Risk” noted: “Data regarding the effects of tea, coffee, and milk on the risk of colorectal cancer are inconsistent. We investigated associations of tea, coffee, and milk consumption with colorectal cancer risk and attempted to determine if these exposures were differentially associated with the risks of proximal colon, distal colon, and rectal cancers.

“Data from 854 incident cases and 948 controls were analyzed in a case-control study of colorectal cancer in Western Australia during 2005–07. Multivariable logistic regression was used to analyze the associations of black tea (with and without milk), green tea, herbal tea, hot coffee, iced coffee, and milk with colorectal cancer.

“Consumption of one or more cups of herbal tea per week was associated with a significantly decreased risk of distal colon cancer, and consumption of one or more cups of iced coffee per week was associated with increased risk of rectal cancer. Neither herbal tea nor iced coffee was associated with the risk of proximal colon cancer. Hot coffee was associated with a possible increased risk of distal colon cancer. Black tea (with or without milk), green tea, decaffeinated coffee, and milk were not significantly associated with colorectal cancer risk.”

The researchers concluded: “Consumption of herbal tea was associated with reduced risk of distal colon cancer, and consumption of iced coffee was associated with increased rectal cancer risk.”

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