• Abstract and Figures
• Public Full-text

ARTICLES Effects of fruit and vegetable consumption on plasma antioxidant concentrations and blood pressure: a randomised controlled trial J H John, S Ziebland, P Yudkin, L S Roe, H A W Neil for the Oxford Fruit and Vegetable Study Group Summary Introduction Ecological and epidemiological evidence suggest that high Background High dietary intakes of fruit and vegetables are consumption of fruit and vegetables is associated with a associated with reduced risks of cancer and cardiovascular reduced risk of cancer1 and cardiovascular disease.2 disease. Short-term intensive dietary interventions in Several mechanisms have been proposed for this process, selected populations increase fruit and vegetable intake, including an increased nutrient intake of antioxidant raise plasma antioxidant concentrations, and lower blood compounds. However, intervention trials of vitamin pressure, but long-term effects of interventions in the general supplements to increase circulating plasma concentrations population are not certain. We assessed the effect of an of antioxidant vitamins have produced little evidence to intervention to increase fruit and vegetable consumption on support this hypothesis.3–6 The health benefits of eating plasma concentrations of antioxidant vitamins, daily fruit and fruit and vegetables may be due, in part, to mechanisms vegetable intake, and blood pressure. other than their antioxidant vitamin content such as blood pressure lowering.7 Current evidence, including Methods We undertook a 6-month, randomised, controlled unpublished trial data (http://www.hpsinfo.org), therefore trial of a brief negotiation method to encourage an increase points to the beneficial effects of eating more fruit and in consumption of fruit and vegetables to at least five daily vegetables rather than vitamin supplementation. portions. We included 690 healthy participants aged An average daily intake of at least five portions of fruit 25–64 years recruited from a primary-care health centre. and vegetables is recommended in the UK,8 which would represent an increase in consumption of 50%9 with only Findings Plasma concentrations of ␣-carotene, ␤-carotene, about 40% of men and women currently achieving this lutein, ␤-cryptoxanthin, and ascorbic acid increased by more target.10 Although short-term intensive dietary inter- in the intervention group than in controls (significance of ventions in highly selected populations increase fruit and between-group differences ranged from p=0·032 to 0·0002). vegetable intake substantially,11,12 raise plasma antioxidant Groups did not differ for changes in lycopene, retinol, concentrations,12 and lower blood pressure,7 whether such ␣-tocopherol, ␥-tocopherol, or total cholesterol interventions are feasible in the general population is concentrations. Self-reported fruit and vegetable intake uncertain. We did a randomised, controlled trial to increased by a mean 1·4 (SD 1·7) portions in the intervention investigate the effect of a 6-month primary-care group and by 0·1 (1·3) portion in the control group (between- intervention to increase fruit and vegetable consumption group difference=1·4, 95% CI 1·2–1·6; p<0·0001). Systolic in a healthy general population with a wide range of eating blood pressure fell more in the intervention group than in habits. controls (difference=4·0 mm Hg, 2·0–6·0; p<0·0001), as did diastolic blood pressure (1·5 mm Hg, 0·2–2·7; p=0·02). Methods Participants Interpretation The effects of the intervention on fruit and We identified all patients aged 25–64 years without vegetable consumption, plasma antioxidants, and blood serious chronic illness from the lists of two general pressure would be expected to reduce cardiovascular practices based in a health centre in Thame, Oxfordshire, disease in the general population. UK. The general practices had few patients from ethnic minorities. We excluded patients with cardiovascular Published online May 28, 2002 diseases (other than hypertension), gastrointestinal http://image.thelancet.com/extras/01art9006web.pdf disease, cancer, serious psychiatric disorders, or hypercholesterolaemia; patients who had undergone a recent traumatic event, such as bereavement; and those unable to give informed consent. We mailed letters to patients sequentially until the target number of patients had been recruited. The letters invited patients to participate in a project giving advice about increasing “natural protective factors” against cancer and heart disease. To ensure that we recruited only one participant Division of Public Health and Primary Health Care (J H John DPhil, from each household we ordered the list by street name P Yudkin DPhil, H A W Neil FRCP) and Imperial Cancer Research Fund and house number, day of month on which born, and General Practice Research Group, Department of Primary Health forename; we invited only the first-named patient at any Care, University of Oxford, Oxford, UK (S Ziebland MSc, L S Roe RD) address to participate. Our intention was to recruit Correspondence to: Dr H A W Neil, Division of Public Health and patients at regular intervals during 1 year to nullify the Primary Health Care, Institute of Health Sciences, University of effects of seasonal changes in food consumption, but Oxford, Headington, Oxford OX3 7LF, UK recruitment actually continued for 14 months (from (e-mail: [email protected]) Aug 1, 1997, to Sept 30, 1998). We excluded respondents THE LANCET • Published online May 28, 2002 • http://image.thelancet.com/extras/01art9006web.pdf 1 For personal use. Only reproduce with permission from The Lancet Publishing Group. ARTICLES who reported using dietary supplements, or who were to ensure that the content and delivery remained pregnant or attempting to conceive. Ethical approval for consistent. the trial was obtained from the Central Oxford Research 2 weeks after the initial intervention, a research nurse Ethics Committee. All participants gave written informed telephoned participants to reinforce the message and consent. discuss any problems. At 3 months, a letter was sent reinforcing the five-a-day message, together with a booklet Procedures of seasonal recipes, and a strategy check list suggesting We allocated eligible participants sequentially to the various ways of incorporating additional portions of fruit intervention or control group with a computer-generated and vegetables into the diet.11 randomisation list. Randomisation was in blocks of four, Controls were randomly assigned to receive the and was stratified by reported smoking status. We invited intervention after 6 months. They received the same participants to attend two appointments at an interval of health check, self-completed questionnaire, and blood 6 months with a trained research nurse at the health sampling as the intervention group. The nurse explained centre. Before each of the two appointments, we mailed that they would receive specific advice at their 6-month participants a self-completion questionnaire. Both follow-up appointment. Controls were asked to carry on questionnaires contained the DINE food frequency as usual until then and were not told that the trial was of a questionnaire13 modified to assess intake of fruit and dietary intervention. At 6-months’ follow-up, they were vegetables and to include “stage of change” questions for given information about the benefits of eating fruit and exercise and intake of fat, fruit, and vegetables.14 vegetables, and offered the same materials as the Questions about fruit and vegetables were embedded intervention group. within other questions to avoid alerting controls to the Primary outcome measures were the between-group nature of the intervention. At the baseline visit, differences in mean individual changes, from baseline to participants were asked about their exercise habits, family 6 months, in plasma concentrations of ␣-carotene, history of premature coronary heart disease and cancer, ␤-carotene, lycopene, ␤-cryptoxanthin, lutein, retinol, and at both visits about smoking. ␣-tocopherol, ␥-tocopherol, and ascorbic acid. Secondary Health checks were done at both visits by study outcome measures were changes in self-reported fruit and research nurses, and included measurement of blood vegetable intake assessed by a dietary questionnaire, pressure (mean of two readings taken 10 min apart with a weight, and blood pressure. 80°C. Lipid-solubleמ Copal UA731 electronic automatic sphygmomanometer We stored plasma samples at [A&D Instruments; Abingdon, UK]), height, and weight vitamin standards and plasma samples were analysed by using a stadiometer and scales. A 10-mL non-fasting the Clinical Trial Services Unit, University of Oxford, venous blood sample was taken for measurement of Oxford, UK, by high-performance liquid chromatography antioxidant vitamins and total cholesterol concentrations. (HPLC) using a Waters system (Waters Corporation; The occupation of patients was recorded and social class MA, USA) fitted with a photodiode array detector. Total was established with the UK Registrar General’s standard cholesterol was measured on a Beckman Synchron CX4 occupational classification.15 clinical chemistry analyser with Beckman reagents Immediately after the health check, the research nurse (Beckman; Brea, CA, USA). Plasma ascorbic acid was introduced the benefits of eating more fruit and vegetables assayed using HPLC17 by the Department of Clinical and presented a pictorial portion guide. A portion was Biochemistry, Glasgow Royal Infirmary, Glasgow, UK. defined as an 80 g serving.

Load more

  6

Copy Link