'Provocative' study could unravel lymphoma mystery

University of NSW epidemiologists have uncovered evidence for an unexpected upside to allergies -- people who suffer from asthma and hay fever are 50 per cent less likely to develop non-Hodgkin's lymphoma.

Individuals who suffer from food allergies are 70 per cent less likely to develop the common blood cancer, which has been on a rapid upward trend during the past three decades. Being an only child also helps -- the incidence of NHL is 50 per cent lower in only children and oldest siblings.

Assoc Prof Andrew Grulich, of the National Centre in HIV Epidemiology and Clinical Research, and lead author on the paper published in the international Journal of the National Cancer Institute, today described his team's finding as "provocative".

The rising incidence of non-Hodgkin's lymphoma -- the form of leukaemia that affected pop singer Delta Goodrem two years ago -- was the driver for the UNSW study. Grulich said NHL is now the third most common cause of cancer deaths in Australia, yet little is known about its cause.

Grulich said NHL was already known to be associated with immune deficiency, and his team wanted to know of immune dysregulation played a role.

Allergies underlie both asthma and hay fever, and Grulich set out to investigate the effect of birth order on the risk of developing NHL. He said the 'hygiene hypothesis' -- the modern obsession with avoiding exposure to disease-causing microbes -- had established an association between being a first-born or only child, and an increased risk of developing allergies, or atopy.

The hygiene hypothesis originated from epidemiological evidence indicating that children who grow up on farms, particularly dairy farms, where they are routinely exposed to microbes through contact with farm animals, manure and dirt.

Such exposure is now thought to have a key role in the maturation of the immune response. The modern obsession with keeping households free of bacteria and other microbes through use of disinfectants and cleaning agents, is now believed to be a key factor in the failure of the immature immune system to develop tolerance to the allergens that cause asthma and hay fever.

Grulich said the new discovery, which came out of an epidemiological study of NHL patients without immune deficiency in NSW and the ACT, supported the case that something important to immune function occurs early in life, probably in the first year.

"The reduction in NHL risk was very similar for both first-born and only children, and this points to something about being on your own for that first year or two," he said.

People with atopic disorders have over-active TH2 T-cells which produce IgE antibodies involved in allergic reaction, which translates to a decreased risk of NHL.

The finding hints that not all exposures to microbes in infancy are necessarily beneficial -- the higher risk of infection that comes from living with siblings, or living less-than-spotless households, may reduce the risk of allergies, but at the cost of a higher risk of developing NHL later in life.

Grulich said his team hopes to confirm the finding through an international collaborative study. Laboratory research work would then be needed to establish why allergies are associated with decreased NHL risk.