A new study, presented at the European Society of Hypertension meeting in London, shows that vitamin D supplementation in winter can help lower blood pressure in patients with hypertension.

Vitamin D is important for a variety of reasons, most notably to help maintain good bone health (it is involved in calcium and phosphorus metabolism), and vitamin D deficiency is associated wide range of diseases including certain types of cancer, depression, diabetes, multiple sclerosis and cardiovascular disease. Although vitamin D is present in some foods, most of our vitamin D is produced in our skin in reaction to sunlight. Many Europeans* have low levels of vitamin D, with this deficiency being particularly acute during the winter months when there is less sunshine. In February when vitamin D deficiency is most common, up to 80% of Danes are deficient. Vitamin D deficiency has been linked with high blood pressure (hypertension), but until now there has been little direct evidence of the benefits of vitamin D to hypertensive patients.

Now a group of Danish researchers have carried out a randomized, placebo-controlled, double-blind study which shows that vitamin D supplements taken during the winter months can help lower blood pressure in hypertensive patients who have low levels of vitamin D. The researchers stress that this is a small study, and that the findings will need to be confirmed by a larger trial.

The researchers studied patients visiting the Holstebro Hospital in Denmark, which is at the 56th Northern latitude (about the same latitude as Glasgow and Moscow). 112 patients (out of an original 130) completed the study. Their initial levels of vitamin D were measured, and then they were given either Vitamin D or a placebo for 20 weeks. 92 of the 112 patients were found to have low levels of vitamin D at the start of the study.

The researchers found that those patients taking the vitamin D supplement showed a significant reduction in central systolic blood pressure (blood pressure measured at the aorta, near the heart), when compared to the placebo group: systolic blood pressure was reduced by 6.8 mmHg, diastolic blood pressure was reduced by 1.7mmHg (see below and abstract for more details).

There was also a reduction in ambulatory blood pressure (blood pressure measured at the upper arm, where several measurements are taken during the day), in those patients who were originally vitamin D deficient, although this reduction was of borderline significance. Commenting, study leader Dr Thomas Larsen said: "Probably the majority of Europeans have vitamin D deficiency, and many of these will also have high blood pressure. What our results suggest is that hypertensive patients can benefit from vitamin D supplementation if they have vitamin D insufficiency. Vitamin D would not be a cure for hypertension in these patients, but it may help, especially in the winter months. However, it is important to stress, that this was a small study, and that larger studies are needed to provide solid evidence."

Commenting, ESH Vice-President, Professor Anna Dominiczak (Glasgow), said: "These results show a significant reduction in Central Systolic Blood Pressure in patients taking the vitamin D supplement for 20 weeks, when compared to the placebo group. This is an initial study, so it needs to be confirmed, but it is potentially interesting as part of an overall strategy for managing hypertension in patients with low levels of vitamin D."

*A recent report estimated that between 50 and 70% of Europeans are vitamin D deficient, see http://www.sciencedaily.com/releases/2012/01/120110102058.htm.