Fruit, vegetable, vitamin A intakes, and prostate cancer risk

Our plain-English summary of Fruit, vegetable, vitamin A intakes, and prostate cancer risk, by G.L. Ambrosini, N.H. de Klerk, L. Fritschi, et al (Prostate Cancer and Prostatic Diseases, 2008).

The study

• Authors: G.L. Ambrosini, N.H. de Klerk, L. Fritschi, D. Mackerras, B. Musk
• Journal: Prostate Cancer and Prostatic Diseases
• Published: 2008;11(1):61-6
• Type of article: Randomized trial
• Cited by: 31 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Prostate cancer risk was examined in relation to intakes of fruit, vegetables, beta-carotene and retinol. Subjects were a cohort of 1985 men previously to asbestos who participated in a cancer prevention programme of beta-carotene and retinol supplements that commenced in July 1990. Diet was assessed at entry to the programme. Ninety-seven cases of prostate cancer were identified during follow-up until the end of 2004. A decreased prostate cancer risk was observed with increasing intakes of vitamin C-rich vegetables, including bell peppers and broccoli. Fruit, other vegetables and vitamin A intakes did not appear to be strong factors in the development of prostate cancer in this study.

In plain English

This study followed 1985 men previously exposed to asbestos who had joined a cancer prevention programme of vitamin A supplements (beta-carotene and retinol) that began in July 1990. Of these men, 49% were former workers and 17% former residents of Wittenoom Gorge in Western Australia, where crocidolite (blue asbestos) was mined and milled, and 34% were exposed to asbestos elsewhere. Their diet was measured once, by questionnaire, when they joined. Over a median of 12.7 years, 97 men developed prostate cancer. Total fruit and vegetable intake, dietary beta-carotene and dietary retinol were not related to prostate cancer risk. Men in the highest third of vitamin C-rich vegetable intake (peppers, broccoli, spinach) had a risk ratio of 0.53 (95% CI 0.29–0.99) compared with the lowest third. For bell peppers alone the figure was 0.46 (95% CI 0.25–0.85). Men exposed to asbestos outside Wittenoom had a higher risk than former Wittenoom workers (risk ratio 2.03, 95% CI 1.22–3.36). The authors concluded that prostate cancer risk did not appear strongly associated with these foods and nutrients, except possibly vitamin C-rich vegetables. They cautioned that some results may have arisen by chance.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Prospective cohort study within a cancer prevention programme in which participants were randomly assigned vitamin A supplements. Diet was assessed at entry, and prostate cancer risk was analysed with Cox proportional hazards models.
• Who was studied: 1985 men (91% of the 2183 men who enrolled in the programme before the end of 1996) who completed a food frequency questionnaire. Of these, 49% were former Wittenoom workers, 17% were former Wittenoom residents and 34% were exposed to asbestos elsewhere. They were followed until 31 December 2004, a median of 12.7 years.
• Exposure: The exposures analysed were intakes of fruit, vegetables, beta-carotene and retinol, estimated from a food frequency questionnaire completed at entry. All participants had past exposure to crocidolite (blue asbestos), mined and milled at Wittenoom Gorge from 1943 until 1966, or occupational crocidolite exposure elsewhere. Source of asbestos exposure was included as a factor in the analyses.
• Main results:
  • After adjustment for age, source of asbestos exposure and assigned vitamin A supplement, total fruit and vegetable intake was not related to prostate cancer risk.
  • Men in the highest third of vitamin C-rich vegetable intake (peppers, broccoli, spinach; more than 4 serves per week) had a risk ratio of 0.53 (95% CI 0.29–0.99) compared with the lowest third. The trend across thirds had a P value of 0.056.
  • For bell peppers, men in the highest third of intake (more than 1.5 serves per week) had a risk ratio of 0.46 (95% CI 0.25–0.85). A trend across thirds was reported (P for trend 0.007).
  • For broccoli, men in the highest third of intake had a risk ratio of 0.56 (95% CI 0.31–1.02). The authors described this as a suggested decrease in risk.
  • Men in the highest third of cooked tomato intake had a risk ratio of 0.67 (95% CI 0.38–1.16). This decrease was not statistically significant.
  • Raw tomato intake, dietary beta-carotene and dietary retinol were not associated with prostate cancer risk.
  • Men exposed to asbestos outside Wittenoom had a higher prostate cancer risk than former Wittenoom workers (risk ratio 2.03, 95% CI 1.22–3.36).
  • Body mass index, smoking status and the randomly assigned vitamin A supplement did not predict prostate cancer risk.
• The authors' conclusion: The authors concluded that prostate cancer risk in this study did not appear strongly associated with intake of beta-carotene, retinol, fruits or vegetables, except possibly with vitamin C-rich vegetables such as peppers and broccoli.
• Limitations the authors state:
  • The questionnaire was designed to measure vitamin A intake. Total fruit and vegetable intake and the fruit and vegetable groups may therefore have been underestimated or misclassified.
  • Diet was assessed only once. Repeated assessments might have improved the study.
  • Taking part in the prevention programme could have changed participants' later eating habits.
  • Because many statistical tests were carried out, some results may have arisen by chance.
  • The analyses could not be adjusted for energy intake, because the questionnaire was not designed to estimate it.
  • The cooked tomato result was possibly not significant because of the study's smaller sample size.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Wittenoom, Western Australia

All asbestos mines

Related studies

• Increased urinary 8-isoprostaglandin F(2)alpha is associated with lower plasma selenium levels and lower vegetable and fruit intake in an asbestos-exposed cohort at risk for lung cancer — E.B. Gottschall, P. Wolfe, et al. (2004)
• Estimated intake of vitamin D and its interaction with vitamin A on lung cancer risk among smokers — T.Y. Cheng, G.E. Goodman, et al. (2014)
• Protective dietary factors and lung cancer — E.T. Fontham (1990)
• Risk of mesothelioma following external beam radiotherapy for prostate cancer: a cohort analysis of SEER database — A. Farioli, F.S. Violante, et al. (2013)
• The role of carotenoids in human health — E.J. Johnson (2002)
• Case-control study of risk factors for prostate cancer — M. Ilić, H. Vlajinac, et al. (1996)

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