Is the Incidence of Rheumatoid Arthritis Rising?

Is rheumatoid arthritis (RA) actually on the rise? Researchers from the Mayo Clinic in Minnesota say “yes”, and they presented data from a study, published in the June issue of the Arthritis & Rheumatism magazine – even though the authors themselves can only speculate about the reasons why.

In that recently published Rheumatoid Arthritis Clinical Study Elena Myasoedova, Cynthia S. Crowson, Hilal Maradit Kremers, Terry M. Therneau, and Sherine E. Gabriel from the Mayo Clinic College of Medicine, Rochester, Minnesota, expanded a previous research from 1955 to 1994, looking at the years 1995 to 2007. To augment the pre-existing study they now focused on the medical records of more than 1,700 residents of Olmstedt County, Minnesota, aged 18 years or older, who had received at least one diagnosis of rheumatoid arthritis (RA).

Yes, RA is on the rise! 

What did they find out? – From 1955 to 1994, the incidence of rheumatoid arthritis had continually been on the decline. That apparently changed beginning in the mid-1990s. When the researchers analyzed patient data from early 1995 to the start of 2005, they found that both the incidence and the prevalence of the condition were rising.

What they found in detail: In the current study, the five researchers found that a RA diagnosis was given to more than 460 patients. Their age was 55.6 years in average, and most of them were women (69%).

Generally speaking, these numbers do fit in what we already knew about rheumatoid arthritis and the epidemiology of this autoimmune disease. But compared to the data of the previous study the current figures deserve closer attention.

Increased incidence in women, decreased in men – environmentally triggered?

Surprisingly, the incidence of RA had increased in women but at the same time decreased very slightly for men. For women, the authors found, the incidence of rheumatoid arthritis increased by 2.5% per year from 1995 to 2007, whereas a decrease of 0.5% per year was seen in men. Applied to the population examined that stands for at least 1.5 million adults now being affected by rheumatoid arthritis (RA), the authors estimated for the entire U.S. population – up from 1.3 million in 1995!

Even the researchers from the Mayo Clinic themselves were not able to explain the observed rise in disease incidence. Because the sudden increase follows decades of decline, it’s too short to a time period to suspect genetic factors, they clarify. They rather suspect a variety of environmental factors, such as cigarette smoking (see my post on this topic: There is a Connection between Rheumatoid Arthritis (RA) and Smoking – what are the Reasons? – posted on 21/05/2010), vitamin D deficiency, or changes in birth control pill formulations.

• Smoking cigarettes: Smoking rates in general have declined in the U.S., but compared to men women have stopped smoking at a lower rate. Maybe this fact explains the slight decrease in men. – Keep in mind: Cigarette smoking is perhaps the strongest environmental risk factor for rheumatoid arthritis! (Concerning this, see blog posts on The Arthritis Support Board and on the Science Blog: Smoking cigarettes is a predictor of RA and may negatively impact on efficacy of anti-TNFs)
• Vitamin D deficiency: Some research has suggested a link between vitamin D deficiency and RA, and vitamin D deficiency has been found to be increasing , especially in women. (more about this in the article Geoepidemiology of autoimmune rheumatic diseases, Nat Rev Rheumatol) and in the post Vitamin D deficiency can lead to rheumatoid arthritis on the Autoimmune Disease Blog). Infections, obesity, immunizations, and socioeconomics status may be other factors explaining the rise of RA in women, the authors describe.
• Lower dose birth control pills: These lower dose pills are increasingly used in favour of those with higher estrogen levels. The higher-dose estrogen pills that were used early on had more of a protective effect for developing RA. As the dose declined, with the same contraceptive benefit the pills provided less protection from rheumatoid arthritis, the study’s authors from Mayo Clinic wrote.

Author of this article:  Tobias Stolzenberg 

Literature:

Myasoedova E, Crowson CS, Kremers HM, Therneau TM, Gabriel SE. Is the incidence of rheumatoid arthritis rising? – Results from Olmsted County, Minnesota, 1955-2007. Arthritis Rheum. 2010 Jun;62(6):1576-82. Rheumatoid Arthritis Clinical Study. – LinkOut to the abstract

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pictures are taken from stock.xchng: cigarette by valikras, The Pill by tijmen – Standard restrictions