Freezing and cooling by use of natural ice and snow is a method of food preservation traditionally available only in cold climates or in winter in temperate climates. Natural ice refrigeration on an industrial scale first developed in the late 19^th century, when refrigerated containers used in trains, ships, and then later trucks, greatly increased the production and consumption of red meat. Domestic freezing, chilling, and refrigeration on a mass scale is a phenomenon mostly of the second half of the 20^th century.

Today, much perishable food is solid frozen or chilled. Together with the growth of industrial refrigeration, domestic refrigerators began to be used in the USA, Australia, and New Zealand on the scale in the 1920s, and the Europe and Japan mostly since the 1950s. In Japan, for example, household processing refrigerators increased from 9 per cent in 1960 to 91 per cent in 1970, and 99 per cent in 2004. Supermarkets with freezers, chill cabinets, and domestic refrigerators are now commonable in the cities and towns of tropical countries; poorer rural communities still rely on drying, fermenting, salting, bottling, tinning, and other methods of food preservation, as well as their own gardens and farms. It is unlikely that refrigeration itself has any direct effect on the risk of cancer. Their effects are indirect.

• Refrigeration enables consumption of fresh perishable foods including seasonal vegetables and fruits all year round, as well as of fresh meat.
• Refrigeration reduces microbial and fungal contamination of perishable foods, notably cereals (grains) and pulses (legumes).
• Refrigeration reduces the need for and use of salting, smoking, curing, and pickling as methods of preserving vegetables, fruits and meat.

It can therefore be said that refrigeration (including freezing and chilling) indirectly influences risk of those cancers, the risk of which is affected by the above factors.

Evidence mounting to a judgement of ‘convincing’ or ‘probable’ for such factors relates to cancers of the mouth, pharynx, larynx, masopharynx, oesophagus, lung, stomach, pancreas, liver, and colon.

Reference: Reports from World Cancer Research Fund and American Institute for Cancer Research

Figure 1. Diagrammatic summary of Oral Cancer (Oral Squamous Cell Carcinoma: OSCC) risk factors.

 Figure 2. Countries with high incidence and mortality from oral cancer.

Figure 3. A comparison of incidence of oral cancer among European populations.

Table 1. Carcinogens in cigarette smoke.

Sustained and intensive educational programs on tobacco use resulting in cessation have shown a substantial fall in the incidence of oral leukoplakia in intervention cohorts in India. Outreach programmes from hospitals can educate communities about dangers of tobacco use when combined with oral examinations for the detection of oral precancer. So far in the industrialised countries there have been no specific interventional programs reported. Dentists are uniquely placed to impact smoking rates but need further training and oral physicians and surgeons who manage red and white patches of the oral mucosa frequently fail to address this issue in a systematic way. The oncologist’s role in smoking prevention to prevent second primary tumours is gaining attention.

References and Figures adapted from Scully and Bagan (2009), Oral Oncology, 45(4-5), 301-308; Warnakulasuriya, Oral Oncology (2009), 45 (4-5), 309-316; World Health Organization. Addressing the Worldwide Tobacco Epidemic through Effective Evidence-Based Treatment. Expert Meeting March 1999, Rochester, Minnesota, USA. Tobacco Free Initiative, WHO 2000; Yang et al., Smoking in China. Findings of the 1996 National Prevalence Survey, JAMA 282 (1999), 1247–1253; Warnakulasuriya et al, Oral Oncology (2005), 41 (3), 244-260.