Written by Partha Nandi, MD, FACP
I get asked some version of the same question in clinic all the time: is cancer just bad luck, or is there something I can actually do about it? A major global study offers the most encouraging answer we have had in years. Roughly 4 in 10 new cancer cases around the world are tied to risk factors you can change, which means there is a real amount you can do to lower your cancer risk.
Researchers with the World Health Organization’s International Agency for Research on Cancer reviewed 18.7 million cancer cases across 185 countries. About 37.8% of them, close to 40%, were linked to modifiable risk factors like tobacco, alcohol, infections, extra body weight, and inactivity. These are associations drawn from population data, not a promise that dropping one habit erases your personal risk. Even so, the takeaway is hopeful: your everyday choices carry real weight.
You don’t need fear or perfection to get started. What helps most is knowing which habits make the biggest difference, so you can bring your risk down with changes that fit your life. Here is where I would start.
Dr. Nandi’s Bottom Line
Close to 40% of cancers worldwide are linked to risk factors you can change, based on a large and credible WHO analysis of real-world data. Smoking, infections, and alcohol lead the list. You can’t erase the genetic hand you were dealt, but you can tilt the odds: don’t smoke, keep alcohol low, stay active, eat mostly plants, protect a healthy weight, keep up with key vaccines, and get screened on time.
What “Nearly 40% Preventable” Really Means
Of the 18.7 million cancer cases studied from 2022, about 7.1 million were tied to 30 risk factors people can influence. The team, led by epidemiologist Hanna Fink, pulled data from 185 countries and matched today’s diagnoses to how common these exposures were years earlier, since cancer usually takes time to develop.
A few things are worth keeping in perspective. These numbers describe associations across large populations, not a guarantee for any one person. The share also shifts by place and sex, from roughly a quarter of cases in some regions to more than half of cases among men in East Asia. The researchers add that the real preventable fraction may be even higher, because some exposures are hard to measure.
Three causes stand out worldwide: tobacco, infections, and alcohol. And just three cancers, lung, stomach, and cervical, account for close to half of every case tied to preventable risks. That is encouraging, because we already know how to cut exposure to the biggest drivers.
Tobacco and Alcohol Top the List
Smoking: still the single biggest cause
Tobacco is the largest preventable cause of cancer on the planet. It was tied to about 15% of all new cancer cases in 2022, and to more than one in five cancers in men. Most people connect smoking with lung cancer, and rightly so, but it also raises the risk of cancers of the mouth, throat, pancreas, bladder, and stomach. If you smoke, quitting is the single highest-impact move you can make for your long-term health, and that holds true at any age.
Alcohol: risk starts with the first drink
Alcohol came in as the second-leading lifestyle contributor, linked to roughly 3% of new cancer cases, which still adds up to hundreds of thousands of diagnoses. It is associated with cancers of the liver, breast, colon, esophagus, and stomach.
Most of my patients are surprised to learn there is no completely safe level of alcohol when it comes to cancer. The World Health Organization places alcohol in the same top-tier carcinogen group as tobacco and asbestos, and the risk begins with the very first drink. As your body breaks down alcohol, it forms acetaldehyde, a substance that can damage DNA. When drinking and smoking happen together, the risk to the upper digestive and respiratory tract climbs higher than either habit alone.
The Infections Behind About 1 in 10 Cancers
After tobacco, infections were the next biggest contributor, linked to roughly 10% of cancers worldwide. Certain viruses and bacteria can trigger long-running inflammation and cellular changes that set the stage for cancer over years.
Two of the most important are human papillomavirus (HPV), which is behind most cervical cancers, and Helicobacter pylori, a stomach bacterium tied to stomach cancer. Hepatitis B and C, which affect the liver, belong on that list too.
The encouraging part is how much of this is already preventable. According to the CDC, HPV causes about 36,000 cancers in the United States every year, and HPV vaccination can prevent more than 90% of them. The vaccine works best when given before exposure, which is why it is recommended for preteens, though older teens and young adults can still benefit. Cervical cancer, once a leading cause of cancer death in American women, is now one of the most preventable cancers we have, thanks to the vaccine paired with regular screening.
Prevention here is not only personal, either. Vaccines, clean water, and access to care protect whole communities at once.
Stress and Behavior: The Indirect Link
Stress does not directly cause cancer in the same way smoking does. However, chronic stress often drives behaviors that increase risk.
When people feel overwhelmed, they may turn to cigarettes, alcohol, overeating, or physical inactivity. Over time, those coping mechanisms accumulate biological consequences.
Chronic stress also affects sleep quality. Poor sleep disrupts immune surveillance, hormone balance, and metabolic health—all of which can influence cancer risk.
Learning to regulate stress through exercise, social connection, mindfulness practices, and adequate rest supports healthier choices overall.
Know Your Personal Risk Profile
While lifestyle changes make a significant difference, prevention is also personal.
Family history, genetic predispositions, occupational exposures, and environmental factors all matter. If you have a strong family history of certain cancers, speak with your physician about earlier or more frequent screenings.
For example:
- Lung cancer screening is recommended for certain individuals with a history of smoking.
- Cervical cancer screening and HPV vaccination significantly reduce risk.
- Colon cancer screening saves lives through early detection.
Screening does not prevent every cancer, but catching disease early dramatically improves outcomes.
The key takeaway is this: you cannot control every mutation in your cells. But you can influence the environment in which those cells live.
My Personal RX on Lowering Your Cancer Risk Day by Day
Cancer prevention comes down to a handful of steady habits that protect your body a little more each day, not a perfect track record. You don’t have to overhaul your whole life this week. Pick one change, make it stick, then add the next.
These are the steps I keep coming back to with patients who want to take real action. None of them need a prescription or a big budget, and together they support the systems that help your body defend itself.
- If you smoke, make a plan to quit. This is the highest-impact step you can take, full stop. Ask your doctor about counseling, nicotine replacement, or a quit-line. You do not have to do it alone, and it is never too late to benefit.
- Rethink your relationship with alcohol. Trim how many days a week you drink, and keep the amounts modest. Swap in sparkling water with lime, herbal tea, or a zero-proof option. Less really is safer here.
- Fill half your plate with plants. Aim for vegetables, fruit, beans, and whole grains at most meals. On busy days when your plate falls short, a scoop of Super Greens is an easy way to add a concentrated dose of antioxidant-rich greens that support your body’s natural defenses.
- Move a little every day. You do not need punishing workouts. A brisk 30-minute walk, light strength work, or time in the garden all count. Consistency beats intensity.
- Build a plan you will actually follow. Lasting prevention comes from a system, not a burst of motivation. My guide, Dr. Partha Nandi’s Protocol for Optimizing Your Health and Wellbeing, walks you through a holistic, day-by-day approach to protecting your heart, brain, gut, and long-term health.
- Protect a healthy weight. Even losing 5 to 10% of your body weight can improve your metabolic health and ease the inflammation linked to several cancers. Small, steady changes beat crash diets every time.
- Stay current on key vaccines. Talk with your provider about the HPV vaccine for yourself or your kids, and about hepatitis B. Preventing these infections can prevent certain cancers down the road.
- Guard your sleep. Aim for 7 to 9 hours. A simple wind-down routine and fewer screens before bed help your immune system do its overnight repair work.
- Find healthy ways to handle stress. Instead of reaching for a cigarette, a drink, or a snack, try breathing exercises, a walk outside, prayer, or time with people who lift you up.
- Keep up with your screenings. Do not put off the colonoscopy, mammogram, Pap, or skin check your doctor recommends. Early detection is one of the most powerful tools we have.
You can’t control everything, but your daily choices carry more weight than most people realize. Start with one, and build from there.
When to See a Doctor
Prevention is powerful, but it does not replace medical care. A few symptoms are worth a prompt look from your doctor. They rarely mean cancer, but catching any problem early gives you the most options. Check in if you notice:
- A new lump, swelling, or thickening anywhere, including the breast or testicle
- Unexplained weight loss, drenching night sweats, or fatigue that won’t lift
- A change in bowel or bladder habits, or blood in your stool or urine
- A sore, mole, or skin spot that changes, bleeds, or will not heal
- A cough, hoarseness, or trouble swallowing that lingers for weeks
- Unusual bleeding, such as between periods or after menopause
If something feels off and won’t settle, trust that instinct and get it checked. You know your body better than anyone.
References:
- Fink, H., Langselius, O., Vignat, J., Rumgay, H., Rehm, J., Martinez, R. X., Santero, M., Lopez-Perez, L., Inoue, M., Zeng, H., Shield, K., Morgan, E., Ilbawi, A., & Soerjomataram, I. (2026). Global and regional cancer burden attributable to modifiable risk factors to inform prevention. Nature Medicine, 32, 1306-1315. https://doi.org/10.1038/s41591-026-04219-7
- World Health Organization. (2023, January 4). No level of alcohol consumption is safe for our health. https://www.who.int/azerbaijan/news/item/04-01-2023-no-level-of-alcohol-consumption-is-safe-for-our-health
- Centers for Disease Control and Prevention. (2026). Screening for colorectal cancer. https://www.cdc.gov/colorectal-cancer/screening/index.html
- Centers for Disease Control and Prevention. (n.d.). HPV infection. https://www.cdc.gov/hpv/parents/about-hpv.html
- Rock, C. L., Thomson, C., Gansler, T., Gapstur, S. M., McCullough, M. L., Patel, A. V., Andrews, K. S., Bandera, E. V., Spees, C. K., Robien, K., Hartman, S., Sullivan, K., Grant, B. L., Hamilton, K. K., Kushi, L. H., Caan, B. J., Kibbe, D., Black, J. D., Wiedt, T. L., … Doyle, C. (2020). American Cancer Society guideline for diet and physical activity for cancer prevention. CA: A Cancer Journal for Clinicians, 70(4), 245-271. https://doi.org/10.3322/caac.21591
Frequently Asked Questions
Can you really prevent 40% of cancers?
Not every individual cancer, but the research suggests close to 40% of cases worldwide are linked to risk factors people can change. Lowering those exposures across a population could prevent a large share of cancers, even though personal risk still depends on genetics and chance.
What is the single best thing I can do to lower my cancer risk?
If you smoke, quitting is the highest-impact step, since tobacco is the leading preventable cause. If you do not smoke, keeping alcohol low, staying active, eating mostly plants, and protecting a healthy weight all help.
Is any amount of alcohol safe?
The World Health Organization says there is no completely safe level of alcohol when it comes to cancer risk. The less you drink, the lower the risk, so cutting back by any amount is a step in the right direction.
Does stress cause cancer?
Stress does not directly cause cancer the way tobacco does. Its effect is more indirect, working through habits like smoking, drinking, overeating, and poor sleep that can raise risk over time.
When should I start cancer screenings?
It depends on the cancer and your personal risk. Most adults at average risk begin colorectal screening at 45, and your doctor can tailor the timing for cervical, breast, lung, and other screenings based on your history.
