A recent study published in the BMC Public Health journal, used data from the Norwegian Women and Cancer study (NOWAC) to explore the effect of changing multiple lifestyle factors during adult life on cancer risk.
Study: Overall lifestyle changes in adulthood are associated with cancer incidence in the Norwegian Women and Cancer Study (NOWAC) – a prospective cohort study. Image Credit: Makistock/Shutterstock.com
Cancer incidence over the years has been a matter of great concern as populations worldwide age, increasing the number of people at risk for this disease.
Many studies have shown that healthy lifestyles are associated with a lower lifetime cancer risk. However, there is a lack of clarity as to whether this can be addressed by changing one's lifestyle in adulthood.
Cancer is responsible for millions of premature deaths worldwide and will soon overtake cardiovascular disease as the number 1 killer.
This will pose an immense cancer burden, with almost 20 million new cases reported in 2020. About 40% of cancer arises from preventable causes, at least in wealthier countries.
The lifestyle factors linked to cancer include a sedentary lifestyle, obesity, smoking, alcohol consumption, and unhealthy dietary patterns.
Cancer prevention has focused on encouraging people to shift towards healthy life patterns. However, there is not much data on how much impact such changes have when they occur in adults with previously unhealthy lifestyles.
An exception is a smoking-related lung and upper digestive tract cancers, known to return to non-smokers' risk levels after smokers quit the habit.
The risk of lifestyle-related cancers drops even more when smoking cessation is combined with dietary intervention in a high-risk group.
Again, stopping alcohol consumption is related to a lower risk of several cancers, while becoming more physically active is associated with a lower risk of colon cancer. Improving cardiovascular fitness is related to lower overall cancer risk than its worsening.
There is a need to understand how changes in multiple lifestyle factors impact cancer risk. Only one such study has been reported, from Sweden, but it did not include dietary intervention despite its obvious importance in cancer risk.
The current study used a large, nationally representative sample of women in Norway. The researchers included two self-reported measures of lifestyle behaviors. These were used to assess the changes in the participants' healthy lifestyle index (HLI) scores.
The researchers then looked for any associations between changes in this score and the cancer incidence for lifestyle-related cancers.
These include those caused by alcohol consumption, tobacco use, obesity-related and those of the reproductive tract, and certain breast and colon tumors.
What did the study show?
The mean age of the participants was 58 years. About half the participants had a physical activity level at or below 6. The mean body mass index (BMI) was borderline high.
About a fifth were current smokers, the median consumption of alcohol was two grams per day, and the diet score was nine the median.
The median HLI score was 13. A mean of seven years elapsed between the first and second self-reported assessment, but there was no correlation between this interval and the extent of HLI score change.
The median follow-up duration was 14 years. There were almost 6,400 cancers during the follow-up period, of which approximately 3,500 and 3,000 were related to alcohol and tobacco consumption, respectively.
Another 3,300 and 2,400 were related to the reproductive tract and the breast, while about 800 each were related to obesity and colorectal cancer, respectively.
During the follow-up, over one in seven (17%) showed zero change in HLI score.
About 16% had a worsening by three points, and the same proportion by one point. Approximately 12% showed a two-point drop. About 12% improved by three points, one in ten by two points, and 15% by one point.
The researchers found that irrespective of the participants' lifestyle at the earlier time, changes towards a healthier lifestyle were associated with a decline in the risk of lifestyle-related cancers, except for those of the breast and colon.
With a 1 SD increase in HLI score, the analysis reflected...
...a 7% lower incidence for lifestyle-related cancers, 4% lower incidence for alcohol-related cancers, 8% lower incidence for tobacco-related cancer, 6% lower incidence for obesity-related cancers, and 10% lower incidence for reproductive-related cancers."
With a drop of three points or more in the HLI score from the baseline, the risk of lifestyle-related cancer rose by 16% overall. With a lifestyle improvement equivalent to a rise by three or more points, the risk fell by 7% or remained stable.
Similarly, as the lifestyle became unhealthier, cancer incidence rose compared to stable lifestyles. Interestingly, this association was more strongly associated with cancer risk than that improved lifestyle behaviors.
Reduced HLI scores were related to a higher incidence of lifestyle-related cancers, but there was no association with increases in the score. A drop by three or more units was associated with a 16% increase in cancer risk.
The changes associated with individual lifestyle factors were <5% compared to changes in all.
The risk for tobacco-related cancers was reduced when the effect of BMI was ignored. There was no effect on the cancer risk by HLI score when stratified by age, even though smoking and drinking trends have changed over the decades.The study claims...
...this increases our confidence that our estimates reflect risk differences largely attributable to HLI score change."
What are the implications?
The analysis supports efforts to encourage a healthier lifestyle shift for women in the age group of 41 to 76 years who are currently unaffected by the disease.
Over various lifestyle patterns at baseline, the cancer risk declined proportionately to the degree of positive lifestyle change.
Of special significance is the proportionate increase in cancer risk as the lifestyle shifted towards the unhealthier side, while it remained stable in the group whose lifestyle did not worsen.
The researchers caution...
...we cannot assert with any confidence that lifestyle improvement is not related to reduced cancer incidence considering the lack of published studies assessing the effects of changes in lifestyle factors in combination. For adult women, maintaining a stable, healthy lifestyle and lifestyle improvement are important for preventing the occurrence of many cancer types."