The study was carried out in nurse run hypertension clinics in six general practices in the Southampton area during 1999-2001.
Inclusion and exclusion
—We included patients aged over 17 not taking hypertensive drugs who had a systolic blood pressure > 160 mm Hg or diastolic > 90 mm Hg from a single reading. These patients should normally be given non-pharmacological advice in primary care during “watchful waiting” before definitive diagnosis of hypertension.1
We excluded patients with established hypertension, renal impairment, regular nonsteroidal anti-inflammatory drugs (which may lead to complications with low sodium salt); patients who were very ill or less able to change diet (for example, severe chronic illness, anorexia, bulimia, pregnancy, breast feeding); and patients with systolic blood pressure > 200 mm Hg or diastolic blood pressure > 120 mm Hg, who it is unethical to observe over months.
—Sample size was determined for α = 0.05, β = 0.2, and took account of guidelines for factorial studies.21
Assuming a standard deviation of 10 mm Hg and that a “factor” changes diastolic blood pressure by 3-4 mm Hg (the “main effect”),17
we required 99 patients for each arm (control; intervention) of a factor. Using 240 patients allowed for 20% loss to follow up.
Randomisation—Several weeks in advance opaque, sealed, numbered randomisation envelopes containing instruction sheets for one group were prepared at the study centre by using random number tables. In each practice, after written informed consent was obtained, subjects were individually randomised to one of eight groups defined by a 2×2×2 factorial design: no booklet or booklet; no advice to use “low salt” or advice to use low sodium salt; and no use of prompts or use of healthy lifestyle prompts.
—We used the British Hypertension Society's booklet Understanding High Blood Pressure
, which includes information about blood pressure and its treatment; nurses highlighted the sections on advice to stop smoking, moderate alcohol intake, reduce weight as appropriate, exercise regularly, and avoid salty foods. Patients were given a pot of low sodium salt (LoSalt; Klinge Foods, East Kilbride) and asked to use it in cooking and on food instead of normal salt, and to get replacements from the supermarket (either the same brand or supermarket own brand). The fatty food swap sheet19
lists, in one column, foods which subjects are asked to swap when shopping and eating with similar but lower fat foods from the other column. The nurse asked the patient to take the sheet when shopping, and keep it in a prominent position at home (fridge, cupboard door). At baseline and four week interview, the nurse asked the patient to use fruit-vegetable-fibre daily prompt sheets.18,20
Each sheet gives options each day for eating fruit and vegetables (for example, an extra portion of fruit, salad, bowl of soup) and fibre (a bowl of cereal a day, or the equivalent in bread); and patients filled in their portions each day.
Instruction sheets—The core content of each consultation and group differentiation was controlled by an instruction sheet. All groups were given a very brief, structured statement about salt, alcohol, weight, and exercise; each group was given its specific statements.
Training—Nurses were trained to use both the equipment and the prompt sheets during a training session.
Follow up—At four weeks and six months, the original interventions were reinforced.
—Outcomes (measured at baseline, four weeks, and six months) were chosen for an effectiveness study—that is, to mimic the assessment that nurses could easily provide in primary care, and thus minimise change in behaviour due to intensive measurements. The primary outcome, blood pressure, was measured by the nurse at one month, three times after the patient had been seated for five minutes, using the Omron HEM-705CP blood pressure monitor.22
were performed by patients, who had been trained by the nurse, after the six month appointment. We also measured several secondary outcomes: serum concentrations of carotenoids (biomarker for fruit and vegetable consumption) and urinary sodium:potassium (Na/K) ratio (for increased potassium and reduced sodium); lipids (cholesterol, high density lipoprotein, low density lipoprotein); food frequency (through a validated questionnaire23
); weight (electronic Seca scales). The final assessment consisted of 14 home measurements of blood pressure, carried out in the patient's home, using the equipment as above; a validated seven day food diary, and a 24 hour urine collection to determine Na:K ratio, with para-aminobenzoic acid to establish completeness of urine collection.23
We measured anxiety with the hospital anxiety and depression scale.
Data entry and analysis—Data were analysed with SPSS and Stata for Windows on an intention to treat basis, with no substitution of missing follow up data. The study was analysed as a factorial study by analysis of covariance for continuous outcomes. The primary outcome was blood pressure at one month, and also change in biomarkers (urinary Na:K ratio and serum concentrations of carotenoids). All other outcomes were secondary. We assessed the estimates for the interactions between factors by statistical models as above, and if no interaction was found the main effects were estimated (that is, the effect of each factor when the effect of other factors was controlled for). Changes of means from baseline were assessed for each variable with the t test.