What is the strength of the cause and effect relationship between alcohol consumption and the development of cancer?

The Causal Relationship Between Alcohol and Cancer

Alcohol consumption has a strong and well-established causal relationship with multiple types of cancer, with evidence showing that consumption of any amount of alcohol increases risk for certain cancers, most notably breast cancer. 1

Strength of Evidence for Causality

The International Agency for Research on Cancer (IARC) has classified alcoholic beverages and ethanol in alcoholic beverages as carcinogenic to humans, with sufficient evidence for causality for multiple cancer types:

• Definitive causal relationship (sufficient evidence):

  • Upper aerodigestive tract cancers (oral cavity, pharynx, larynx, esophageal squamous cell carcinoma)
  • Liver cancer
  • Colorectal cancer
  • Female breast cancer 1

• Probable causal relationship:

  • Stomach cancer 1

Magnitude of Risk

The risk increases with the amount of alcohol consumed:

• Heavy alcohol consumption (≥4 drinks/day) increases risk approximately:

  • 5-fold for oral/pharyngeal cancer and esophageal squamous cell carcinoma
  • 2.5-fold for laryngeal cancer
  • 50% for colorectal and breast cancers
  • 30% for pancreatic cancer 2

• Even low alcohol consumption (≤1 drink/day) increases risk by:

  • 20% for oral and pharyngeal cancers
  • 30% for esophageal squamous cell carcinoma 2
  • For breast cancer, even 3-6 drinks/week may yield a small increase in risk 2

Mechanisms of Alcohol Carcinogenesis

Multiple biological mechanisms explain alcohol's carcinogenic effects:

• DNA and protein damage from acetaldehyde (ethanol's primary metabolite)
• Oxidative stress and inhibition of DNA repair
• Increased cell proliferation
• Nutritional malabsorption
• Changes in DNA methylation
• For breast cancer: increased estrogen levels
• Introduction of carcinogenic contaminants during beverage production 1

Public Health Impact

The cancer burden attributable to alcohol is substantial:

• In the United States (2014), alcohol consumption caused:

  • 5.6% of all incident cancer cases
  • 4% of all cancer deaths
  • 40.9% of oral cavity/pharynx cancers
  • 23.2% of larynx cancers
  • 21.6% of liver cancers
  • 21% of esophageal cancers
  • 12.8% of colorectal cancers
  • 16.4% of breast cancers in women (39,060 cases) 1

• Globally (2016), alcohol caused:

  • 376,200 cancer deaths (4.2% of all cancer deaths)
  • 10.3 million cancer disability-adjusted life years lost 3

Synergistic Effects

Alcohol interacts synergistically with tobacco use, increasing the risk of upper aerodigestive tract cancers considerably more than either drinking alcohol or tobacco use alone 1. The combined effect is greater than the sum of their individual effects 1.

Recommendations

Based on the strong causal relationship between alcohol and cancer:

• The American Cancer Society recommends: "It is best not to drink alcohol." 1
• For those who choose to drink, limit consumption to no more than:
  • 1 drink per day for women
  • 2 drinks per day for men 1

Important Considerations

• There is little evidence of a threshold effect for oral, pharyngeal, and esophageal cancers, meaning even small amounts increase risk 2
• Women with high risk for breast cancer might reasonably consider abstaining completely from alcohol 1
• The proportion of cancer deaths attributable to alcohol varies by age, ranging from 13.9% among people aged 30-34 years to 2.7% among people aged 80-84 years 3
• Despite potential cardiovascular benefits of moderate alcohol consumption, the World Health Organization has concluded that "consuming zero standard drinks daily minimizes the overall risk to health" 1

The evidence clearly establishes alcohol as a direct cause of multiple cancers, with risk increasing in proportion to consumption and no safe threshold for certain cancer types.