Cardiovascular disease is a major cause of mortality throughout the world . Both morbidity and mortality can be reduced by improving individuals' cardiovascular risk profile by, for example, preventing hypertension, lowering blood pressure in hypertensive people, increasing physical activity (PA) and fruit and vegetable consumption, and reducing saturated fat intake [1–9]. International public health guidelines have been developed for reducing the risk of cardiovascular diseases. Based on these, the Dutch guidelines recommend that Dutch people consume at least two pieces (approximately 200 grams) of fruit and 200 grams of vegetables a day, be moderately physically active at least 5 days a week for at least 30 minutes a day, and have a maximum saturated fat intake of 10% of their total energy intake [1, 7, 10–15].
Various studies have shown that large percentages of adults fail to meet these public health recommendations [16–23]. De Vries and colleagues  showed that more than half of Dutch adults fail to meet the PA guideline, that 69.5%, 86.2% and 38.9% fail to meet the guidelines for fruit, vegetable and fat intake respectively and that only 3% adhere to all guidelines for PA, fruit, vegetable and fat intake, and smoking. Thus, interventions are needed to improve these health behaviors.
Computer tailoring and motivational interviewing (MI) are both innovative and promising intervention methodologies that are being used to improve health behaviors. Tailoring has been defined as "any combination of information or change strategies intended to reach one specific person, based on characteristics that are unique to that person, related to the outcome of interest, and have been derived from an individual assessment" (p. 1) . Computers are useful tools to tailor messages for large groups of people at low costs . Research has reported that computer tailoring has a positive effect on PA [26–30], fruit and vegetable consumption [26, 31–38] and saturated fat intake [39, 40], also compared to generic information on changing these behaviors [27, 33, 37, 40, 41].
MI is defined as "a client-centered, directive method for enhancing intrinsic motivation to change by exploring and resolving ambivalence" (p. 25) . Evidence exists of the effectiveness of MI on PA [43–45], fruit and vegetable consumption [46–48] and saturated fat intake [49, 50], and also when compared to standard advice on changing these behaviors [45, 47, 48, 50].
Research into tailoring emphasizes the need to compare these methods with others concerning their effects on changing behavior [25, 51]. The Vitalum study contributes to this need. Its design was inspired by the NC STRIDES Project, which compared the effects of computer tailoring to those of MI in a colon cancer prevention and control study on PA and fruit and vegetable consumption in participants aged 50 or older [52–54]. Vitalum examines the efficacy of computer tailoring and MI on PA, fruit and vegetable consumption and saturated fat intake in participants aged 45 to 70 with and without hypertension. We also assess Vitalum's efficacy for different education levels since health disparities between SES groups are increasing  and health behavior adoption varies between these groups [56, 57].
Older adults are an important target group for research and the development of lifestyle interventions for several reasons. First, adults between 45 and 70 represent more than 20% of the population in European countries . Second, this percentage is likely to increase in the coming years . Third, most blood pressure-related deaths or nonfatal events occur in middle age or in the elderly providing a cue to action for this age group . Finally, older adults are important targets for prevention because health improvements due to increased PA, fruit and vegetable consumption, and lowered saturated fat intake still contribute to reduced risk of morbidity and mortality rates in this group [1, 7, 60].
When Vitalum began in 2003 no results were available of studies that compared the economic consequences of interventions using computer tailoring and motivational interviewing. Physical inactivity, consuming too little fruit and vegetables and eating too much saturated fat may result in disease and loss of quality of life [8, 61]. Therefore, Vitalum also aims to evaluate and compare the cost-effectiveness of computer tailoring and motivational interviewing.
This article describes the Vitalum study design, which may help others in developing of equivalent interventions.