First of all, your numbers are good, but they depend on when one was born, and are higher for younger people:
The lifetime risk of cancer increased from 38.5% for men born in 1930 to 53.5% for men born in 1960. For women it increased from 36.7 to 47.5%. Results are robust to different models for projections of cancer rates.
Trends in the lifetime risk of developing cancer in Great Britain: comparison of risk for those born from 1930 to 1960
(This is for Great Britain, but at least for the US and similar countries, I don't expect too much deviation)
Cancer Research UK has done a bit of legwork as it relates to your question. Their rough estimate is that 4 out of 10 cancers are preventable through a healthy lifestyle. From their section on preventable cancers:
- Smoking is the largest single cause of cancer in the UK, linked to an estimated 19% of cancer cases in the UK each year. Lung cancer has the highest proportion of smoking-linked cases.
- Diet (too little fruit, vegetables and fibre; too much red and processed meat and salt) is linked to an estimated 9% of cancer cases in the UK each year. Upper aero-digestive tract cancers (oral cavity and pharynx, oesophageal, and larynx) have the highest proportion of diet-linked cases.
- Overweight and obesity is linked to an estimated 5% of cancer cases in the UK each year. Uterine, kidney and oesophageal cancers have the highest proportions of bodyweight-linked cases.
- Alcohol is linked to an estimated 4% of cancer cases in the UK each year. Upper aero-digestive tract cancers (oral cavity and pharynx, larynx, and oesophageal) have the highest proportion of alcohol-linked cases.
That's about 37 percent, all added up. They have more information on all these on the website I linked.
I did a bit of looking around myself, just to see.
The main cancer risks for males are:
- Prostate, at about 15 percent
- Lung, at about 7.5 percent
- Colon, at about 5 percent
- Bladder, at about 4 percent
- Skin, at about 2.5 percent
- Non-Hodgkin lymphoma, at about 2 percent
- Kidney, at about 2 percent
That adds up to about 38 percent.
Let's see how lifestyle factors impact them.
For prostate cancer, the four factors you link possibly don't have an impact. Diet might be involved, but we don't really know how:
Men who eat a lot of red meat or high-fat dairy products appear to have a slightly higher chance of getting prostate cancer. These men also tend to eat fewer fruits and vegetables. Doctors aren’t sure which of these factors is responsible for raising the risk.
For lung cancer, smoking is of course the major risk factor. For non-smokers, risk of lung cancer is reduced by about 85 to 90 percent
For colon cancer, about half of the cases are linked to lifestyle.
For bladder cancer, about half of the cases are linked to smoking alone.
Skin cancer is caused by sun exposure, but also genetic disposition.
The risk factors for non-hodgkins-lymphoma are unknown.
For kidney cancer, risk factors include obesity and smoking, with an estimated 40 percent of the risk coming from lifestyle factors.
So, as a back of the envelope calculation, if the risks for prostate and non-hodgkins-lymphoma don't decrease, the lung cancer risk decreases by about 90 percent, and the other listed cancer have a risk decrease of about half, we end up with about 25 percent of the original 38 percent for these 7 cancer types. A reduction of 35 percent.
The main cancers differ for females:
- Breast, at about 12 percent
- Lung, at about 7 percent
- Colon, at about 4.5 percent
- Uterine, at about 3 percent
All others are below 2 percent. These four add up to 26.5 of the lifetime risk.
The relationship between breast cancer and lifestyle factors seems to be complicated, with it maybe being linked to obesity and also linked to number of children.
About 40 percent of Uterine cances are linked to obesity.
Lung and colon cancer were also on the list for males. Another back of the envelope calculation reduces the risk of these four cancers from 26.5 to 16.5 percent. A reduction of 38 percent.
- These are very rough calculations
- These are based only on lifetime risk of developing cancers, not lifetime risks of dying from cancers
- We really don't understand cancer all that well for many of them
- the cancers I didn't list here, like bladder/cervix/pancreatic cancer also make up quite a few percent of the lifetime cancer risk, combined