--- title: What Causes Cancer? 40% of Cancers Can Be Prevented description: Scientists calculated that four in 10 cases of cancer are caused by modifiable risk factors, such as smoking or lack of exercise canonical: https://time.com/5032099/what-causes-cancer-risk-factors/ author: Alice Park article:opinion: false article:content_tier: free article:published_time: 2017-11-21T15:00:25.000Z article:modified_time: 2026-02-23T18:19:01.517Z article:section: Health og:title: Nearly Half of Cancer Cases Are Within Your Control, Researchers Say og:description: Smoking is the biggest modifiable risk factor og:url: https://time.com/5032099/what-causes-cancer-risk-factors/ og:site_name: TIME og:image: https://static.time.com/v3/assets/bltea6093859af6183b/blt11e539440670afa3/6988c135ab6d7793a76ad785/time-health-stock-first-air-kit.jpg?branch=production&width=1200&quality=75&auto=webp&crop=16:9 og:image:width: 5000 og:image:height: 2813 og:image:alt: time-health-stock og:type: article twitter:card: summary_large_image twitter:title: Nearly Half of Cancer Cases Are Within Your Control, Researchers Say twitter:description: Smoking is the biggest modifiable risk factor twitter:image: https://static.time.com/v3/assets/bltea6093859af6183b/blt11e539440670afa3/6988c135ab6d7793a76ad785/time-health-stock-first-air-kit.jpg?branch=production&width=1200&quality=75&auto=webp&crop=16:9 ---  # Nearly Half of Cancer Cases Are Within Your Control, Researchers Say > Sponsored content. 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Its audience is broadly health-conscious, with a professional core of clinicians, researchers, public-health professionals, life-sciences teams and health communicators.  by [Alice Park](https://time.com/author/alice-park/)  ## Alice Park Senior Correspondent Nov 21, 2017 3:00 PM UTC  First aid kit on blue background with copy space First aid kit on blue background with copy space Getty Images  by [Alice Park](https://time.com/author/alice-park/)  ## Alice Park Senior Correspondent Nov 21, 2017 3:00 PM UTC Diseases as complicated as cancer are often caused by genetic factors that are out of your control and risk factors that you can change. Now, researchers have calculated just how much of that risk is within a person’s control. In a [study published in _CA: A Cancer Journal for Clinicians_](http://onlinelibrary.wiley.com/doi/10.3322/caac.21440/full), researchers led by Dr. Farhad Islami at the American Cancer Society analyzed national cancer data and calculated how much of cancer cases and deaths can be attributed to factors that people can change. These included smoking, exposure to second-hand smoke, being overweight or obese, drinking too much alcohol, eating red and processed meats, eating too few fruits and vegetables, not exercising, exposure to ultraviolet radiation through activities like tanning and six cancer-related infections (including HPV). Among more than 1.5 million cancers in 2014, 42% were traced to these factors, as well as 45% of deaths in that year. Cigarette smoking accounted for 20% of the cancer cases: the largest contribution by a modifiable risk factor. Overweight or obesity was the second-greatest contributor, accounting for nearly 8% of cases and 6.5% of deaths. Alcohol accounted for 5.6% of cases and 4% of deaths; red and processed meat consumption contributed to 1.3% of cases and deaths, and not exercising enough accounted for 2.9% of cancer cases and 2.2% of deaths. Eating too few fruits and vegetables — which applies to [around 90% of Americans](http://time.com/5029164/fruit-vegetable-diet/) — was responsible for nearly 2% of cancers and 3% of cancer deaths. **MORE:** [The FDA Just Approved a New Way of Fighting Cancer Using Personalized Gene Therapy](http://time.com/4989537/blood-cancer-gene-therapy/) The data are sobering, especially because [deaths from cancer have dropped](http://time.com/4622645/cancer-death-rates/) by 25% since 1991\. While that’s good news, the latest data suggest that the decline might be even steeper if people address some of their risky behaviors that contribute to cancer. About 600,000 people are expected to die of cancer in 2017. Islami says that the study should be seen as encouraging overall, since it supports the idea that a good proportion of cancer cases and deaths might be avoided. While factors such as alcohol and lack of exercise accounted for a much smaller percentage of cases and deaths than smoking, for example, together they have a sizable effect on cancer risk. The combination of excess weight, alcohol, poor diet and lack of exercise contributed to nearly 14% of cancer cases in men and 22% in women. For women, that contribution was greater than the effect of smoking. “If \[people\] avoid some of these risk factors, they could substantially reduce their risk of many types of cancer,” says Islami. He hopes that the findings encourage local, state and federal lawmakers to support more policies that reduce these modifiable risk factors, such as creating smoke-free areas, constructing walkable communities and encouraging physical activity. He says that doctors can also learn lessons from the data, since studies show that people are more likely to change their behaviors if their doctors inform them of how risky they might be. ```json [{"@context":"https://schema.org","@type":"NewsArticle","@id":"https://time.com/5032099/what-causes-cancer-risk-factors/","mainEntityOfPage":{"@type":"WebPage","@id":"https://time.com/5032099/what-causes-cancer-risk-factors/"},"headline":"Nearly Half of Cancer Cases Are Within Your Control, Researchers Say","datePublished":"2017-11-21T15:00:25.000Z","dateModified":"2026-02-23T18:19:01.517Z","description":"Scientists calculated that four in 10 cases of cancer are caused by modifiable risk factors, such as smoking or lack of exercise","url":"https://time.com/5032099/what-causes-cancer-risk-factors/","keywords":["Cancer","Diet & Nutrition","healthytime"],"thumbnailUrl":"https://static.time.com/v3/assets/bltea6093859af6183b/blt11e539440670afa3/6988c135ab6d7793a76ad785/time-health-stock-first-air-kit.jpg?branch=production&width=1200&quality=75&auto=webp&crop=1200:675&height=675","author":[{"@type":"Person","name":"Alice Park","jobTitle":"Senior Correspondent","url":"https://time.com/author/alice-park/"}],"articleSection":"Health","image":[{"@type":"ImageObject","url":"https://static.time.com/v3/assets/bltea6093859af6183b/blt11e539440670afa3/6988c135ab6d7793a76ad785/time-health-stock-first-air-kit.jpg?branch=production&width=1200&quality=75&auto=webp&crop=1200:675&height=675","width":1200,"height":675,"headline":"time-health-stock","caption":"First aid kit standing on a blue and white background TIME health stock","creditText":"Getty Images","representativeOfPage":true}],"publisher":{"@type":"Organization","name":"Time","url":"https://time.com/","logo":{"@type":"ImageObject","url":"https://time.com/images/logo.png","width":528,"height":156},"foundingDate":"March 3, 1923","sameAs":["https://www.facebook.com/time","https://www.instagram.com/time/?hl=en","https://twitter.com/time","https://www.pinterest.com/timemagazine"]}},{"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"item":{"@id":"/section/health/","name":"Health"}},{"@type":"ListItem","position":2,"item":{"@id":"/tag/cancer/","name":"Cancer"}},{"@type":"ListItem","position":3,"item":{"@id":"https://time.com/5032099/what-causes-cancer-risk-factors/","name":"Nearly Half of Cancer Cases Are Within Your Control, Researchers Say"}}]}] ```