The two-year study, from the University of Navarro in Spain, followed 6000 patients eating a Mediterranean diet, with its particularly high intake of monosaturated fatty acids.
"This is the first study that showed an inverse association between the consumption of low-fat dairy products and incident hypertension," reported lead author Alvaro Alonso.
"A diet rich in low-fat dairy products resulted in a greater decrease in blood pressure than did a low-fat comparison diet, which supports the beneficial effect of low-fat dairy consumption for the prevention of hypertension."
There are an estimated 10m people in the UK with hypertension, defined as having blood pressure higher than 140/90 mmHg. High fat diets have long been identified as a prime factor in increasing the risk of hypertension. This has led to a switch by many consumers to lower fat products.
In the UK, semi-skimmed, or half-fat milk, now accounts for 60 per cent of total milk sales. Skimmed milk is also growing in popularity, now accounting for a further 14 per cent of the total.
The Spanish researchers now suggest that special proteins in milk actually cut the risk of hypertension in a way that is countered when the full fat content is retained.
"Milk proteins - both caseins and whey proteins - are a rich source of angiotension converting enzyme inhibitory peptides. In animal models, these proteins… have been shown to significantly reduce blood pressure," Alonso writes in the November issue of the American Journal of Clinical Nutrition (vol 82, no 5, pp972-979).
"It is plausible that saturated fats in whole-fat dairy products somehow neutralize the beneficial effect of dairy protein."
The research followed volunteers with an average age of 37, adjusting its results for other nutritional factors including caffeine, sodium, alcohol, and fibre intake.
"We showed that the beneficial effect of low-fat dairy consumption is not restricted to young adults and obese persons," it concluded.