Citrus fruits and cancer: what the evidence says and does not say

Do citrus fruits prevent cancer?

Not in the way this is often presented. The evidence comes from observational studies: thousands of people are asked what they eat, followed for years, and researchers see who develops cancer. The World Cancer Research Fund’s authoritative report concludes that eating fruit and non-starchy vegetables probably reduces the risk of several digestive and respiratory cancers [1]. These include cancers of the mouth, pharynx and larynx, oesophagus, stomach, lung, colon and rectum. For each cancer considered separately, the evidence is limited. Citrus fruits are part of that fruit intake, but the conclusion concerns the overall pattern, not oranges specifically.

When citrus fruits are examined separately, the figures are modest. A meta-analysis of 21 studies published in Pharmacological Research in 2021 compared people who ate the most citrus fruit with those who ate the least. In the former group, the risk of lung cancer was 9% lower. The lowest risk was observed at around 60 g a day, a little more than half an orange. Above about 80 g a day, the risk did not fall further [2].

Here is the limitation of these studies: association is not causation. People who eat fruit every day tend to smoke less, be more physically active and eat fewer ultra-processed foods; studies adjust for some of these factors, but never all of them. That is why none of these figures allows us to say that a glass of juice a day protects you: they indicate that eating fruit is part of a lifestyle associated with less cancer.

Why can no single food prevent cancer on its own?

Because cancer does not depend on just one thing. Smoking, alcohol, excess body fat, physical activity, age, genetics and chance all affect risk, and diet matters as an overall pattern, not as an individual food. A review of prospective studies published in the International Journal of Epidemiology in 2017 shows this well. For every 200 g of fruit and vegetables eaten daily, the overall risk of cancer fell by around 3%. At about 600 g a day, it stopped falling [3]. This is a real but small effect. The groups with the clearest association with cancer overall were green and yellow vegetables and cruciferous vegetables, such as broccoli and cabbage [3].

Concentrating the beneficial parts of fruit into a capsule does not work either. Limonoids and flavonoids in citrus fruits have mainly been studied in laboratory cells and animals, and this does not allow us to make claims about people. The World Cancer Research Fund recommends getting what you need from food and not using supplements to prevent cancer. In trials, supplements have not reproduced the results observed in dietary studies. The beta-carotene supplements studied increased the risk of lung cancer in people who smoked or had smoked [1]. If you need a supplement, your doctor or dietitian-nutritionist should advise you.

Does grapefruit interact with chemotherapy and other medicines?

Yes, it interacts with some medicines, and this is the most useful point to take away from this page. According to the US Food and Drug Administration (FDA), grapefruit and its juice block an intestinal enzyme called CYP3A4 [4]. This enzyme helps break down certain medicines before they enter the bloodstream. Blocking it can allow more of a medicine than expected to enter the blood and increase side effects. The FDA’s list includes medicines for cholesterol, blood pressure, heart rhythm and anxiety. It also includes corticosteroids and medicines that prevent transplant rejection. With some antihistamines for allergies, the opposite happens: less of the medicine enters the blood, so it is less effective [4]. The agency warns that bitter orange, pummelo and tangelo may have the same effect as grapefruit [4].

This matters in oncology because many treatments are no longer given only through a vein: some chemotherapy and targeted therapies are taken as tablets at home. A review published in Frontiers in Pharmacology in 2021 examined oral cancer medicines that are eliminated through this pathway [5]. It classifies grapefruit juice as a moderate inhibitor that acts mainly in the intestine. In the case of sunitinib, the measured effect was small. In other words, it depends on the medicine; your oncology team or pharmacist is the person who can tell you whether yours is affected.

The practical advice is simple. If you take medication regularly, ask your pharmacist or doctor whether grapefruit interacts with it; do not change your medication on your own. Until you have asked, avoid grapefruit and its juice, and read the patient information leaflet, as the FDA recommends [4]. If you have been eating grapefruit without knowing about this, do not panic: mention it at your next appointment, or sooner if you notice new side effects, and do not stop or change your medication on your own.

Can I drink orange juice during chemotherapy?

Generally, yes, if it agrees with you and your team has not told you otherwise: the FDA warning focuses on grapefruit and similar citrus fruits [4]. What changes during treatment is tolerance. If you have mouth sores, acidic foods can sting, so it is better to leave citrus fruits until they improve. With nausea, some people find acidic flavours easier to tolerate than anything else, while others find they upset their stomach: go by what you notice.

Advice for managing each side effect, from mouth sores to loss of appetite, is in our guide to eating during cancer treatment. For overall guidance on what to eat at this stage, see our diet guide for people with cancer.

One safety point: if you have been told that your immune defences are low, wash fruit thoroughly under running water before peeling or cutting it. Ask your team before drinking unpasteurised juices. The FDA warns that people with cancer and weakened immune systems are at greater risk of becoming seriously ill from unpasteurised juices [6]. Your team will tell you whether you need any further precautions.

How can you include citrus fruits in your everyday diet without becoming fixated on them?

Like any other fruit: eat a variety, choose what is in season, and have it whole rather than as juice where possible, because whole fruit retains its fibre and is more filling. In winter, this is easy: have a mandarin mid-morning, an orange cut into segments for dessert, or squeeze lemon over fish or salad. The zest of a well-washed lemon or orange adds flavour to yoghurt, homemade cake or roasted vegetables without adding salt.

What makes a difference is the overall pattern: fruit and vegetables at every meal, pulses, whole grains, little alcohol and daily physical activity. It is the same pattern that helps preserve muscle and bone as you get older, as we explain in our longevity guide.