Compared to adults without shingles, those who suffer from it were more likely to suffer a stroke within a year of the attack. Patients who had shingles in and around an eye had 4 times the risk of stroke in the year following the episode.

The study included nearly 8,000 adults treated for shingles between 1997 and 2001 and about 23,000 people matched for age and sex who had no history of shingles or stroke before 2001.

During the year following the shingles episode, 133 shingles patients and 306 people in the comparison group had strokes.

The shingles patients had a 31% increased risk of strokes of any kind, and a nearly 3 times increased risk of haemorrhagic strokes. Patients with shingles involving the skin around the eye and the eye itself were 4.28 times more likely to have a stroke than were people without shingles.

Haemorrhagic strokes, caused by bleeding in the brain, are much less common than ischaemic strokes, which are caused by blocked arteries. Only about 10% to 15% of strokes involve brain bleeds.

Previous studies have shown an elevated stroke risk associated with shingles, but this is the first study to quantify the risk.

Stress and inflammation may play a role

Varicella zoster virus-related blood vessel damage has been linked to stroke after shingles attacks, but this did not fully explain the high stroke risk seen in the study, say the researchers.

They added that the stress associated with shingles, and the intense pain that can occur with outbreaks and following shingles due to nerve damage could play a role, as could the inflammation that occurs with shingles outbreaks.