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Orange juice and grapefruit linked to melanoma skin cancer

1:30pm Wednesday 1st July 2015 content supplied byNHS Choices

"Drinking a glass of orange juice or eating a fresh grapefruit for breakfast may increase the risk of skin cancer," the Mail Online reports.

A US study did find a small increase in the risk of melanoma, but the benefits of unsweetened fruit juice shouldn't be overlooked.

A glass (150ml) of fruit juice counts as one of your recommended five daily portions of fruit and vegetables, which in turn can protect against a range of chronic diseases.

The US study involved more than 60,000 female and 40,000 male health professionals. Participants were asked to fill out a questionnaire every two to four years about their diet, lifestyle and incidence of skin cancers.

An increased risk of melanoma was found for those who drank more than a glass of orange juice a day, as well as for people who ate fresh grapefruit more than three times a week.

These findings do appear to find a link between citrus fruit and skin cancer risk. But this type of study cannot prove cause and effect.

While researchers attempted to adjust their results for potential underlying factors, such as age, other factors could also have influenced the results. For example, people who live in sunnier parts of the US, such as Florida or California, may also consume more citrus fruits.

By taking a number of commonsense sun-safe precautions, you can have the best of both worlds - enjoying citrus fruit while not significantly raising your skin cancer risk.

These include making sure you wear sunscreen and appropriate clothing, and staying indoors during periods of intense sunlight.   

Where did the story come from?

The study was carried out by researchers from Brigham and Women's Hospital, Harvard Medical School and Brown University, and was funded by a grant from the National Cancer Institute.

It was published in the peer-reviewed Journal of Clinical Oncology.

These findings have been reported reasonably accurately by the Mail Online. But some caution should be taken when reading the Mail's article, as this study cannot prove causation and there are other health benefits associated with eating fruit. It does, however, provide advice on how to detect skin cancer, which is very useful.  

What kind of research was this?

These were two prospective cohort studies with a long follow-up. The studies aimed to investigate whether citrus products may be associated with an increased risk of melanoma. Melanoma is an aggressive type of skin cancer that can spread to other parts of the body.

Citrus products are known to contain high levels of a chemical compound called psoralen, which absorbs ultraviolet light.

Psoralen drugs are used for the treatment of skin conditions such as psoriasis, but animal studies and long-term use of the drugs in people have shown it may increase the risk of melanoma.

This type of study is unable to prove citrus products cause melanoma, but it could find possible links for future investigation. 

What did the research involve?

The study included 63,810 women in the Nurses' Health Study and 41,622 men in the Health Professionals Follow-Up Study, both of which ran from the mid-1980s to 2010.

Every two to four years, people answered detailed questionnaires on their diet, lifestyle and levels of sun exposure. Data on melanoma diagnosis was collected and confirmed with medical records - this included tumour stage and location.

The participants answered questions about how frequently they consumed grapefruits, oranges, grapefruit juice or orange juice.

The total of these four categories was considered an estimate of overall citrus consumption, although it did not include other citruses such as lemons and limes.

Melanomas were classified into two subgroups according to location:

  • high continuous sun exposure - head, neck, extremities
  • low continuous sun exposure - shoulders, back, hips

Various analyses were performed and adjusted for known melanoma risk factors and potential confounders. Subgroup analyses were performed to assess the influence of common medications, healthy diet and sunscreen use. 

What were the basic results?

Over an average of 24 to 26 years of follow-up, there were 1,840 cases of melanoma. Participants with higher citrus intake were less likely to smoke cigarettes and drink coffee, were more likely to exercise, and had a higher intake of individual citrus products and vitamin C.

After adjustments were made for potential risk factors and confounders, there was an increased risk of 36% observed for overall citrus consumption of more than 1.6 times a day, compared with less than twice a week in the reference group (hazard ratio [HR] 1.36, 95% confidence interval [CI] 1.14 to 1.63).

Fresh grapefruit showed the strongest link, with a 41% increased risk for those who eat fresh grapefruit more than three times a week compared with those who never ate grapefruit (HR 1.41, 95% CI 1.10 to 1.82). This association was not seen for consumption of grapefruit juice.

statistically significant association was found between grapefruit consumption and melanomas on sites with higher continuous sun exposure.

Consuming orange juice more than once a day had a 25% increased risk of melanoma compared with less than once a week (HR 1.25, 95% CI 1.07 to 1.47). Eating oranges alone did not have a significant effect on melanoma risk.

No associations were found for other fruits and vegetables and the risk of melanoma.  

How did the researchers interpret the results?

The researchers concluded that, "Citrus consumption was associated with an increased risk of malignant melanoma in two cohorts of women and men.

"Nevertheless, further investigation is needed to confirm our findings and explore health-related implications." 

Conclusion

This study aimed to assess the association between psoralens found in citrus fruit and melanoma risk.

A link was observed between orange juice, fresh grapefruit and overall citrus consumption, with grapefruit causing the highest level of increased risk. The researchers say this is because there are higher levels of psoralens in grapefruits than other citrus fruits.

The strengths of this study are its prospective design, large sample size and long-term follow-up.

However, the sample was composed of US health professionals, who may have very different diet and lifestyle habits from most US citizens, which limits the generalisability of the findings.

As participants were required to fill out a questionnaire, this may be subject to recall bias. There were also wide confidence intervals, which reduces the certainty of the results, especially given the large number of participants.

These findings should be taken with caution as they are unable to prove citrus consumption is the cause of melanoma. Fruit intake is known to have beneficial effects on the prevention of chronic diseases. Further investigation is required to confirm this risk.

A positive association was seen for those who had higher sunburn susceptibility as a child, more blistering sunburn episodes, spent more time in direct sunlight, and those with a higher annual UV flux at their home. This may have been the cause of the increased melanoma risk rather than the effect of citrus fruit. 

These findings really stress the importance of taking care in the sun by wearing sunscreen and appropriate clothing, and staying indoors during periods of intense sunlight.

Read more about how to prevent melanoma, a particularly aggressive type of skin cancer that kills more than 2,000 people every year in the UK. 

Summary

"Drinking a glass of orange juice or eating a fresh grapefruit for breakfast may increase the risk of skin cancer," the Mail Online reports. A US study did find a small increase in the risk of melanoma, but the benefits of unsweetened fruit juice.

Links to Headlines

Is there a link between orange juice and SKIN CANCER? 'Citrus fruits may increase the risk of melanoma', study declares. Mail Online, June 30 2015

Links to Science

Wu S, Han J, Feskanich D, et al. Citrus Consumption and Risk of Cutaneous Malignant Melanoma. Journal of Clinical Oncology. Published online June 29 2015

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