Over six million cancers diagnosed worldwide each year may be preventable by avoiding known risk factors, such as maintaining healthy diet, avoiding excess weight gain, staying active, and avoiding alcohol and smoking.

High cancer burden in Australia/New Zealand and worldwide

Over 18 million cancers are diagnosed and nearly 10 million deaths worldwide each year (>166,000 cases and >57,000 deaths in Australia and New Zealand), excluding nonmelanoma skin cancers.¹ Each year Australians and New Zealanders lose over 880,000 and 127,000, respectively, years of healthy life due to cancer.^{2 3} Economic cost is also high: for example in Australia >$6.3 billion in health system costs⁴ and >$1.7 billion in productivity losses⁵ annually, at least 0.5% of gross domestic product.⁶

Three to four in every ten of these cancer cases^{7 8 9} and deaths⁷ are preventable by avoiding known risk factors. These include lifestyle exposures, such as diet, physical activity, overweight and obesity, alcohol and smoking, which we will concentrate on in this article.

Eat a healthy diet

Relationships between specific nutrients and food groups and the risk of cancer have attracted significant research attention and public interest. The strength of the evidence in this field remains an ongoing debate, as most studies are observational and subject to similar biases (for instance, diet being hard to measure, and associated with other lifestyle factors), which meta-analysis does not overcome.^{10 11} Nevertheless, the World Cancer Research Fund (WCRF)’s latest evidence summary and recommendations for cancer prevention (2018)¹² identified a number of dietary exposures as probable or convincing risk factors for individual tumour streams. Their interactive cancer matrix¹³ is a useful resource for clinicians working in this space that outlines individual risk factors in relation to cancer risk. One key diet recommendation is that wholegrains, vegetables, fruit and legumes should form a major part of our diet. There is suggestive evidence that regular fruit and non-starchy vegetable intake (recommendation: at least five servings, or 400g/day) and adequate fibre intake (recommendation: 30g/day from food) may reduce risk of several gastrointestinal cancers and possibly others including breast cancer.¹² Red meat (whilst a good source of protein, iron and other nutrients) has consistent evidence of a link to increased colorectal cancer and so should be limited to three portions/week (350–500g cooked weight), cooked to avoid charring; processed meats, also strongly linked to elevated colorectal cancer risk, should be reduced or eliminated.¹² Dairy products and dietary calcium are probably protective against colorectal cancer^{10 12} and possibly premenopausal breast cancer.¹² Fewer studies convincingly link dietary factors and gynaecological cancer, apart from consistent evidence indicating that coffee may decrease endometrial cancer risk while glycaemic load may increase risk.¹²

Recent movement towards evaluating dietary patterns (combinations of foods within a diet) has high clinical value, given food groups and nutrients are consumed in combination. Evidence from prospective studies shows high adherence to a Mediterranean diet (a largely plant-based diet with low levels of red meat)¹⁴ is associated with decreased risk of many cancers including liver and gastric,¹⁵ while a single trial suggested decreased breast cancer risk.¹⁶ There is strong evidence that healthy or ‘prudent’ dietary patterns, also heavily weighted towards vegetables and wholegrains, may substantially reduce the risk of some cancers including colorectal and breast, with less evidence for gynaecological cancers.¹⁷ Conversely, meta-analyses suggest Westernised dietary patterns (high in processed foods, refined grains, added sugar, and low in fruits, vegetables and fibre) are associated with increased risk of cancers including colorectal, breast, and endometrial.^{17 18 19}

There are many mechanisms likely to explain the associations between diet and cancer risk (including gut dysbiosis, inflammation, epigenetic changes, oxidative stress, insulin resistance and hormone metabolism),²⁰ but one key pathway involves the role of a healthy diet in helping to avoid overweight and obesity. Following the WCRF dietary recommendations noted above, and their additional recommendations to avoid sugar-sweetened beverages and reduce intake of ‘fast’ and other processed foods high in sugar, fat, and starch, will put you in good stead to achieve a healthy body weight.

Maintain a healthy body weight

The International Agency for Research on Cancer have determined that maintaining a healthy body weight (usually defined as body mass index [BMI] of 18.5–24.9 kg/m2) is beneficial for reducing the risk of at least 13 cancer types,²¹ with overweight/obesity the second biggest preventable cause of cancer.⁸ Each 5kg/m2 increment in BMI is associated with a seven-fold increase in endometrial cancer, a nearly five-fold increase in oesophageal adenocarcinoma, and approximately 10% increases in postmenopausal breast cancer and ovarian cancer.²¹ Mechanisms linking excess adiposity and cancer risk are likely to include metabolic dysfunction, chronic inflammation and sex hormones.²²

Keep active: move more, sit less

Another daily choice that we can make to lower cancer risk, and a key WCRF cancer prevention recommendation, is staying active by doing regular physical activity and minimising time spent in sedentary activities (for example, computer use, driving or watching TV).¹² Physical activity is any movement needing more energy than resting, including aerobic activity, such as jogging or cycling, or anaerobic activity (resistance training) such as weightlifting. Exercise scientists often measure activity intensity by comparing oxygen uptake to resting rate, classifying activities as sedentary (sitting or reclining); light (standing or slow walking); moderate (e.g. brisk walking, with heart/breathing rates ~60–75% of maximum), and vigorous (e.g. running or team sports, with heart/breathing rates >75% of maximum). There is consistent evidence that vigorous activity reduces pre- and postmenopausal breast cancer, and that greater overall physical activity decreases risk of multiple cancers, especially oesophageal, colon, endometrial, and breast (particularly postmenopausal) cancer; risk reductions range up to 40% comparing most- and least-active people.^{12 23} We know less about sedentary time, but evidence is accumulating that it probably increases risk of endometrial and other (perhaps colon, lung) cancers, independent of physical activity; however compounding by other unhealthy behaviours such as smoking remains an issue, and understanding interactive effects of physical activity and sedentary behaviour is an ongoing research effort.²²

The WCRF cancer prevention recommendation is to meet or exceed national guidelines on activity. In Australia and New Zealand (in line with many other countries), adults are recommended to do >75 minutes of vigorous or >150 minutes of moderate aerobic physical activity (or a combination) every week, plus muscle-strengthening activities two days per week, and to limit and break up sedentary time.^{24 25} Lifestyles which are physically active and lifestyles involving high levels of sedentary time are not mutually exclusive; for instance, people meeting physical activity guidelines may also have long continuous periods of screen time.²² Therefore lifestyle modifications should consider both. People could consider active commuting and recreation, walking meetings, setting regular ‘stand and stretch’ reminders during sedentary activities, and using wearable activity trackers.

Being active and minimising sedentary time promote conditions less conducive to tumour initiation and growth; they may reduce cancer risk by helping to maintain a healthy weight (of strong relevance for endometrial cancer), but also more directly by reducing levels of sex hormones (e.g. of relevance for hormone-sensitive cancers including breast), improving metabolic function including insulin sensitivity, improving/preventing states of chronic inflammation including lowering adipokine levels, improving immunity, reducing oxidative stress, or reducing digestion time (likely of relevance for colorectal cancers).^{22 23}

Eliminate alcohol

Alcohol intake is classified by the International Agency for Research on Cancer as a confirmed carcinogen and is a key contributor to the global burden of cancer. Alcohol use is associated with >200 health conditions and causes over 3 million deaths annually worldwide, 0.4 million (13%) from cancers.²⁶ There is strong evidence that alcohol causes many cancers, including in the breast, liver, and multiple gastrointestinal tract sites, and building evidence suggests a causative role in others; risks range up to fivefold higher (oral, pharyngeal, oesophageal cancers; higher for women) for heavy drinkers versus nondrinkers.^{12 27} There is no safe level of alcohol of any type from a cancer prevention perspective, so not drinking alcohol is another key WCRF prevention recommendation.¹² The International Agency for Research on Cancer curates a useful website, Cancers Attributable to Alcohol,²⁸ for further information. Explanatory mechanisms are still under active research and may include carcinogenicity of ethanol metabolites, epithelial damage in the upper digestive tract, immunosuppression, and increases in sex hormone levels.²⁷

Avoid smoking

Tobacco smoke has long been classified a carcinogen with compelling evidence of carcinogenicity, and is the largest contributor to cancer incidence worldwide.^{7 8 29} Tobacco use (smoked or smokeless) is a cause of many cancers, including most aerodigestive/gastrointestinal cancers particularly lungs and throat, bladder, kidney, liver and cervical cancer, and myeloid leukemia.²⁹ Over 80% of lung, 70% of larynx and 50% of oesophageal cancers are attributable to smoking;^{8 29} all of these cancers have low survival rates. Smokers are at highest risk of lung cancer: current and ex-smokers have over eight- and four-fold, respectively, higher risk than never-smokers.³⁰ Quitting reduces risk by 30–50% after 10 years, relative to continued smokers.²⁹ Whilst Australia and New Zealand have seen a steady decline in smoking thanks to national public education campaigns and high taxes on tobacco products, 8–16% of young adults still smoke daily and rates continue to be higher in disadvantaged and regional areas.^{31 32} The Royal Australian College of General Practitioners guidelines and New Zealand Ministry of Health guidelines for smoking cessation offer key practical recommendations tailored to individual patient preferences, with nicotine replacement therapy plus behavioural support offering the most promising strategy.^{33 34}

Conclusion

The burden of cancer in Australia and New Zealand is high, yet 30–40% of all cancers, and up to 80% of specific cancers, are preventable. Maintaining a healthy diet and weight, being physically active, and eliminating alcohol and smoking are the cornerstone cancer prevention recommendations from the WCRF (and will lower risk of many other chronic diseases). While addressing individual- and system-level barriers to adopting healthy lifestyles is required, implementing these recommendations as a collective may offer synergistic and multifaceted prevention strategies that are low cost and can reduce burden from a wide range of cancers. Active and timely referral to allied health professionals (i.e. nutrition, exercise, and psychological expertise) to support behavioural change along with continual education and awareness-raising around these modifiable lifestyle risk factors will help reduce the burden of cancer in Australia and New Zealand.

Our feature articles represent the views of our authors and do not necessarily represent the views of the Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG), who publish O&G Magazine. While we make every effort to ensure that the information we share is accurate, we welcome any comments, suggestions or correction of errors in our comments section below, or by emailing the editor at [email protected].

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