Cancer Risk & Your Genes: Can lifestyle trump inheritance?
Cancer is a disease that starts in the DNA of your genes. But that doesn’t mean your cancer risk is unchangeable.
Last week I was speaking at the American Society on Aging’s annual conference, talking about how – even for older adults — lifestyle choices can reduce cancer risk. People I met at the conference were eager to hear about how aging, heredity and lifestyle choices fit together affecting risk of cancer.
Genetic does not mean pre-determined
All cancer is “genetic” – it’s caused by malfunction of genes controlling cell growth and reproduction. But most people talking about cancer as “genetic” make untrue assumptions.
♦ Does this mean cancer risk is mostly inherited?
Unlike inheriting genes for red hair or brown eyes, no more than 5 to 10 percent of cancer risk is inherited.
♦ Does this mean cancer risk is unchangeable?
Research now shows it’s not just the genes you inherit that affect cancer risk. Eating habits, physical activity and other lifestyle choices seem to turn on and turn off genes, such as tumor suppressor genes, that affect cancer risk.
The “hardware” and “software” of genes & cancer risk
We used to focus on DNA itself as the key to cancer risk. It’s been clear for some time that only a small proportion of cancers could be linked to inherited genes that put someone at very high risk of a specific cancer. But researchers looked at how particular genes might make some people more sensitive to the cancer-promoting influence of certain environmental or lifestyle cancer risks. And they studied how permanent changes in genes – mutations – could be a key to cancer risk.
♦ Tiny changes in the building blocks of our DNA create genetic changes (which researchers call SNPs) that make some people more affected by these influences than others. For example, protective compounds in broccoli and other cruciferous vegetables may offer some people more protection than others, and red meat may pose extra hazard for people with certain genes. Testing can identify some of these genetic changes that matter, but we are far from knowing all gene differences. That’s why, for now, recommendations to reduce cancer risk are intended for all.
♦ One way that antioxidant nutrients and phytochemicals may protect us is by preventing DNA damage and helping repair damage that does occur.
As important as it is for a computer to have good hardware – like the hard drive and memory that determine how well a computer can run – software is critical in determining what the computer actually does. If our genes’ DNA is the hardware, scientists have discovered a whole new world in looking at epigenetics, which might be compared to your computer’s software. They’ve learned that without changing the building blocks of the DNA itself, many influences can change how genes are expressed, and the results are potentially life-changing.
- Compounds in garlic and onion, and other compounds in cruciferous vegetables (such as broccoli, Brussels sprouts and cabbage), can make changes in protective genes that have become “turned off” over time. As these compounds turn the genes back “on”, this allows inactivation of carcinogens and promotes self-destruction of abnormal cells prone to develop into cancer.
- Although damage that changes DNA itself is permanent, what’s special about these epigenetic changes in turning genes “on” and “off” is that these changes are reversible.
Epigenetics means, “it’s not too late”
The reversibility of turning genes off and on has important implications:
- Leading a healthy lifestyle in your early years doesn’t guarantee that protective genes remain in their optimal form when you’re older. Just because you’re over 50 or over 65, it’s no time to “coast” on those healthy habits now.
- On the other hand, if your lifestyle in earlier years was not so healthy, it looks as though smart choices in your eating habits and activity level can turn on expression of protective genes. Lifestyle changes can promote healthier levels of hormones and reduce inflammation, creating an environment within your body that helps reduce your cancer risk.
Observational studies that follow people over many years identify multiple lifestyle choices linked with lower likelihood of developing cancer. If you’re middle-aged or older, can changes you make now reduce your cancer risk?
This is a difficult question to study, because most cancer develops over many years. Researchers would need to be able to follow a huge pool of people who actually stuck with a recommended eating pattern or lifestyle.
What’s easier to accomplish is to see if changing lifestyle can change certain markers of cancer risk that research has identified. The answers look promising.
♦ Polyps are the starting point of most colon cancer. Originally, the Polyp Prevention Trial, in which people who’d already had one colon polyp were taught to reduce their fat intake and significantly boost vegetable, fruit and overall fiber consumption, seemed to offer no benefit. But when researchers went back and looked only at the people who actually met the goals of the eating plan all four years of the study, these people showed 35 percent lower recurrence of colorectal polyps.
♦ Research in the diabetes field shows that when people at high risk of developing type 2 diabetes changed eating habits, added regular physical activity and lost some of their excess weight, their odds of developing diabetes were reduced almost 60 percent at three years, and even at 10 years, by 34 percent. Researchers found that the intervention was “exceptionally effective” in those aged 60 to 85 at the start of the study. Type 2 diabetes is associated with increased risk of several types of cancer, and the reduction in insulin resistance seen in trials like this means that the cancer-promoting influence of insulin and insulin-like growth factors also change.
♦ Chronic low-grade inflammation increases risk for heart disease and seems to create a body environment in which cancer is more likely to develop. Overall research suggests that healthy eating habits, such as a Mediterranean-style or DASH diet, can lead to drops in markers of inflammation. When healthy eating choices also promote weight loss in people who are overweight, inflammation tends to drop even more successfully.
♦ Researchers are avidly studying the potential for changes in our eating habits to change our digestive tract microbiota – the trillions of bacteria there – and thus protect the colon from cancer and perhaps even lower risk of cancer elsewhere in the body. Some types of bacteria seem to produce substances that protect our cells, while other bacteria produce substances that seem to be harmful. The types of bacteria that live in our gut seem to be influenced by several factors, and thus vary from person to person. Studies now suggest that changes in our diet can change gut hormones and inflammation within weeks.
Bottom line: Growing research shows that our eating and lifestyle choices throughout life have impact on our risk of developing cancer. “The sooner, the better” for healthy eating and physical activity habits. Yet, especially with growing evidence on the importance of epigenetics, “better late than never” is an important message we need to share about cancer risk.
To read more about our genes, cancer risk and what we can do to lower cancer risk, check this free brochure from the American Institute for Cancer Research (AICR): A Closer Look at Nutrigenomics.
For a brief video interview with Dr. Stephen Baylin, MD, Investigator with The Cancer Genome Atlas (TCGA), click here for an explanation of the difference between Genetics and Epigenetics.
For an in-depth lecture, Cancer Epigenetics by Peter Laird, check this from The Cancer Genome Atlas (TCGA) Scientific Symposium 2011. Note that this is aimed primarily for scientists and health professionals, and focuses on one type of epigenetic change, methylation of DNA.
Sansbury LB et al. The effect of strict adherence to a high-fiber, high-fruit and -vegetable, and low-fat eating pattern on adenoma recurrence. Am J Epidemiol. 2009 Sep 1. 170(5):576-84.
Diabetes Prevention Program Research Group, Crandall J et al. The influence of age on the effects of lifestyle modification and metformin in prevention of diabetes. J Gerontol A Biol Sci Med Sci. 2006 Oct. 61(10):1075-81.
Nordmann AJ et al. Meta-analysis comparing Mediterranean to low-fat diets for modification of cardiovascular risk factors. Am J Med. 2011 Sep. 124(9):841-51.
Nowlin SY et al. Diet, inflammation, and glycemic control in type 2 diabetes: an integrative review of the literature. Nutr Metab. 2012. 2012:542698.
Davis CD and Milner JA. Gastrointestinal microflora, food components and colon cancer prevention. J Nutr Biochem. 2009 Oct;20(10):743-52.