Arthritis Ireland Arthritis Ireland

A new study has shown that the number of women being diagnosed with rheumatoid arthritis rose between 1995 and 2007 in the US.

Scientists at the Mayo Clinic analysed the medical records of 1,761 adults from Minnesota, all of whom had been diagnosed with a form of arthritis (not including degenerative arthritis and osteoarthritis).

Of these, 466 patients had rheumatoid arthritis - 69 per cent of whom were female - and researchers found that the average age at diagnosis was 55.6 years.

Lead researcher Dr Sherine Gabriel confirmed: "We observed a modest increase of rheumatoid arthritis incidence in women during the study period, which followed a sharp decline in incidence during the previous four decades."

Analysis showed that rheumatoid arthritis incidence increased by 2.5% in women between 1995 and 2007, but fell by 0.5% in men.

The study authors, whose findings are published in the journal Arthritis & Rheumatism, believe that the increase in incidence among women may be linked to environmental factors such as smoking, vitamin D deficiency and oral contraceptive use.

Smoking rates are declining at a much slower rate in women than in men in the US, while modern oral contraceptives contain much lower doses of oestrogen - which provides protection against rheumatoid arthritis - than their predecessors.

Meanwhile, a growing body of evidence supports a link between vitamin D deficiency and the development of rheumatoid arthritis, and this deficiency has become more common among women in recent years.

Dr Gabriel observed: "Reasons for the increase in incidence we found are unknown, but environmental factors likely play a role and should be further explored."