FRUIT AND VEGETABLE INTAKE AND BLOOD PRESSURE
INCREASED FRUIT AND VEGETABLE CONSUMPTION IS ASSOCIATED WITH A DECREASE IN BLOOD PRESSURE AFTER SEVERAL WEEKS
High fruit and vegetable intakes are associated with lower blood pressure in cross-sectional studies(1-4). The decrease in blood pressure associated with the increase of fruit and vegetable intakes is shown in experimental studies(5-6).This decrease in blood pressure is observed after several weeks of dietary change and is maintained until the end of follow-up in experimental studies (6 months maximum).
In the DASH study(5) the systolic blood pressure (SBP) of 154 adults who were randomly assigned to eat a strict diet rich in fruit and vegetables decreased by 2.8 mm HG compared to the control group after 8 weeks. John et al(6) observed a decrease of 4 mm HG in subjects who were encouraged to increase their fruit and vegetable consumption to at least five servings per day after 6 months of follow-up. Experimental studies have shown that increased fruit and vegetable intakes in addition to other dietary behaviour modifications such as reduced sodium or increased dairy product consumption, also have an effect on blood pressure(7-9). Theses results support the hypothesis that an increase in fruit and vegetable intake reduces blood pressure over a short-term period and this effect is maintained after several months of consumption.
Many components of fruit and vegetables are thought to be involved in the process of lowering blood pressure; the role of fibre(10), potassium, calcium and magnesium(11) has been confirmed in experimental studies. Results from intervention trials on vitamin or antioxidant supplementation effects are, however, less conclusive(12). These results support the hypothesis that an increase in fruit and vegetable intake reduces blood pressure but since follow-up periods in experimental studies to date have been limited to only several months, less is known about the long-term effects of increased fruit and vegetable intake over a period of several years(13).
COULD LIFE-LONG HIGH FRUIT AND VEGETABLE INTAKE SLOW THE RISE OF BLOOD PRESSURE (ASSOCIATED) WITH AGEING?
The rise in SBP with age is a phenomenon observed world-wide(14). However, very specific populations are not affected(15) by this increase, suggesting that environmental factors such as diet could be highly involved. Recently published(16-18) cohort studies suggest that fruit and vegetables could function as protective factors against this increase. In the Framingham Children's Study(16), children initially aged 3 to 6 years who ate more than 4 servings per day of fruit and vegetables had a comparatively lower increase in blood pressure by early adolescence: their mean SBP was 106 mm HG compared to 113 mm HG in the other children after a follow-up of 8 years. In the Chicago Western Electric Study(17), fruit and vegetables were associated with a lower increase in blood pressure in men initially aged 41 to 57 (in 1958) after seven years of follow up. In the SUVIMAX study (1995 to 2001) which included men and women aged 36 to 62 years at baseline, the increase in blood pressure was reduced by 2.2 mm HG in the highest quintile of fruit and vegetable consumers compared to the lowest quintile(18). Fruit intake was also associated with a lower risk of incident hypertension in the CARDIA study(19).
POTENTIAL MECHANISMS OF A LONG-TERM EFFECT
The potential mechanisms of the long-term effects of fruit and vegetable intakes on the increase in blood pressure remain unclear and may be different than those involved in short-term decreases in blood pressure. In the SU.VI.MAX study, daily antioxidant supplementation was found to have no effect on the risk of hypertension(20) compared to placebo, suggesting that long-term changes in blood pressure may not be explained by antioxidant activity alone but by other fruit and vegetable components such as fibre. It is also likely that the negative association observed in cohort studies may be explained by confounding factors. For example, high fruit and vegetable consumers often have healthier behaviours which may not be completely controlled for when adjusting variables in observational studies. Only a long-term (several years or more) controlled trial could demonstrate the protective effects of fruit and vegetable intakes on blood pressure increases associated with ageing. This is hardly feasible with dietary interventions.
In conclusion, numerous studies recommend high fruit and vegetable intakes in order to have a protective effect on blood
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