Access to clean drinking water is essential to health. However, drinking water can be contaminated by harmful substances, including arsenic. Agricultural, mining and industrial practices can contaminate water with arsenic. Arsenic can also occur naturally in water due to natural geological deposits or volcanic activity.
The International Agency for Research on Cancer (IARC) has judged drinking water contaminated with arsenic to be carcinogenic to humans. The primary regions where high concentrations of arsenic have been measured in drinking water include large areas of Bangladesh, China and West Bengal (India).
Maté is an infusion (brewed using boiling water), which is drunk almost exclusively in parts of South America. It is a type of herbal tea prepared from the dried leaves of the plant Ilex paraguariensis. Maté is traditionally drunk scalding hot through a metal straw. Drinking very hot beverages such as mate is graded by IARC as probably carcinogenic to humans.
Coffee and tea
Coffee and tea are the two most commonly consumed hot drinks. Coffee is made from ground, roasted coffee beans – the dried seeds of coffee plant berries. Many different qualities, varieties and forms of coffee are available. These include arabica and robusta coffee beans, roasted or green coffee beans, as well as instant coffee and soluble powders made from finely ground coffee beans.
There are also various different methods of preparing coffee depending on culture and personal preference. Decaffeinated coffee is produced by various processes, using water, organic solvents or steam, or by interfering with the expression of the gene coding for caffeine.
Tea is specifically the infusion of the dried leaves of the plant Camellia sinensis. Green tea, which is often preferred in China, is made from leaves that have first been cooked, pressed and dried. To produce black tea, the fresh leaves are withered, rolled repeatedly, allowed to turn deep brown and then air-dried until they are dark in colour.
Evidence on whether consumption of milk affects the risk of cancer is considered in the section on Meat, fish and dairy.
Sugary or sweetened drinks
Consumption of sugar-sweetened drinks is a cause of weight gain, overweight and obesity. However, there is no direct link to cancer risk. For more on this, see the section on Energy balance and body fatness.
There is no strong evidence in humans to suggest that artificially sweetened drinks with minimal energy content, such as diet sodas, are a cause of cancer.
OUR MAJOR FINDINGS ON THIS EXPOSURE
There is strong evidence that:
Recommendations have not been made about coffee as there are still too many unanswered questions.
A global recommendation about consumption of mate has not been made as this is consumed only in specific parts of the world. Nevertheless, the Expert Panel of scientists who judged the evidence advises that mate should not be consumed scalding hot in the traditional style.
There is no global recommendation for arsenic in drinking water, as individuals do not have the power to control whether or not their local water supply is contaminated. However, contamination of water supplies with arsenic is a public health issue. Authorities should ensure that safe water supplies are available when such contamination occurs. Water contaminated with arsenic should not be consumed.
All about water
Access to clean drinking water is essential to health.
The water content of the body is around 70 per cent: men tend to have a higher proportion of water in their bodies than women, because women naturally have more body fat, which has minimal amounts of water.
Drinking water can contribute to intakes of essential elements, such as calcium, iron and copper, depending on its origin and the piping materials used. It can also be used as a vehicle to provide fluoride.
Even mild dehydration (water loss of one to two per cent of body weight) can produce symptoms such as a dry mouth and headaches. Stopping all fluid intake causes death in days, with the exact length of time depending on the health of the individual and environmental conditions such as temperature and humidity.
Approximately 80 per cent of water intake comes from drinks; food provides the other 20 per cent.
Environmental conditions, health, activity levels and other factors determine the amount of water needed, but there is no international recommendation for daily consumption. The Institute of Medicine in the USA recommends 2.7 litres per day total water for women and 3.7 litres for men. Public Health England advises to drink six to eight glasses of fluid a day, around 1.2 litres, to prevent dehydration. Water, lower-fat milk and sugar-free drinks including tea and coffee all count.
Adults produce an average of around 1.5 litres of urine each day. An additional litre of water is lost through breathing, from the skin by evaporation or sweating, and in the faeces.
Arsenic in drinking water
Lung, bladder, skin and kidney cancers: the mechanisms linking arsenic in drinking water with cancer development are poorly understood. Experimental studies suggest that exposure to arsenic and its metabolites induces production of reactive oxygen species inducing DNA damage, altering transcription factor function, and modulating the expression of genes involved in cell growth, survival and cancer risk.
Maté and oesophageal cancer
Any carcinogenic effects of maté are believed to be due to consumption at very hot temperatures (over 65°C), increasing the incidence of nitrosamine-induced tumours.
Maté and cancer of the mouth, pharynx and larynx
Any carcinogenic effects of mate are believed to be due to consumption at very hot temperatures (over 65°C), which can cause chronic mucosal injury that can promote tumorigenesis. Repeated thermal injury has been shown to promote upper oesophageal carcinogenesis in rodent studies, supporting this proposed mechanism.
Coffee and liver cancer
Coffee is rich in a large number of bio active compounds including caffeine, chlorogenic acids and numerous phenolic compounds. Emerging evidence suggests that these compounds may have beneficial effects on the liver ranging from antioxidant, anti-inflammatory properties to the inhibition of angiogenesis, but the main underlying mechanisms of the role of coffee in liver cancer development are not fully elucidated.
Coffee is also associated with improved insulin sensitivity, decreased incidence of metabolic syndrome and reduced level of liver injury, which could represent additional mechanisms by which coffee drinking may reduce the risk of liver cancer development.
Coffee and endometrial cancer
The mechanisms linking coffee consumption to a decrease in endometrial cancer risk remain unclear but may involve lower circulating levels of bioavailable sex steroids or insulin and higher insulin sensitivity in people who drink coffee. Coffee drinking is correlated with higher levels of sex hormone-binding globulin (SHBG), which may decrease exposure to bioavailable oestradiol levels.
A large cross-sectional study of more than 1,200 women in the Nurses’ Health Study reported that in premenopausal women, coffee intake was associated with lower luteal phase total and free ostradiol levels, while in postmenopausal women caffeine and coffee intake were positively associated with SHBG levels.
Coffee drinking is also associated with reduced insulin levels, particularly among overweight women, and it has been hypothesised that coffee may reduce the risk of endometrial cancer through an insulin-mediated mechanism. Coffee has also been shown to alter adipokines and inflammatory pathways and lead to an increase in adiponectin levels – an adipokine that is down-regulated in obesity and has been linked to endometrial cancer development
Coffee and cancers of the mouth, pharynx and larynx
The biological mechanisms specifically linking coffee consumption to reduced risk of cancers of the mouth, pharynx and larynx are unclear. Coffee drinking provides exposure to a range of biologically active compounds, many of which have been demonstrated to target pathways associated with carcinogenesis in a variety of tissues. For example, phenolic phytochemicals such as the antioxidants caffeic acid and chlorogenic acid have both been shown to inhibit DNA methylation in vitro.
Coffee is also a source of natural diterpenes, such as cafestol and kahweol, which have been shown to induce apoptosis and have anti-oxidative and anti-inflammatory effects. However, there is a paucity of experimental data on the effects of coffee and its constituent compounds specifically on cancers of the mouth, pharynx and larynx.
Coffee and skin cancer
The exact biological mechanisms linking coffee consumption to malignant melanoma and basal cell carcinoma are uncertain. Coffee drinking provides exposure to a range of biologically active compounds, many of which have been demonstrated in in vitro and animal studies to have anti-oxidant and anti-tumorigenic properties.
These include high levels of certain phenolic phytochemicals, such as the anti-oxidants caffeic acid and chlorogenic acid, and natural diterpenes, such as cafestol and kahweol, which have been shown to inhibit changes in DNA methylation, induce apoptosis, and have anti-oxidative and anti-inflammatory effects.
Tea and bladder cancer
Tea is a rich source of biologically active compounds, including polyphenols. Animal models have shown that certain polyphenols found within green tea inhibited bladder cancer tumour growth. However, more evidence is required to assess any possible anti-tumorigenic role of tea consumption on bladder cancer.