NEWS - Birth order, allergies tied to risk of lymphoma

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Birth order, allergies tied to risk of lymphoma

Last Updated: 2005-04-22 11:38:13 -0400 (Reuters Health)

NEW YORK (Reuters Health) - Both allergies and a person's place in the

sibling pecking order may influence the risk of developing the blood cancer

non-Hodgkin lymphoma, new study findings suggest.

Australian researchers found that people who were either elder siblings or

only children had relatively lower risks of developing non-Hodgkin lymphoma,

or NHL. A similar protective effect was seen among people with a history of

hay fever or food allergies.

The researchers speculate that early immune system development may be behind

all of these associations. In brief, early infection -- more likely with

multiple kids in a family -- may set the immune system in such a way that

allergies don't develop; but on the other hand this setting may increase the

chances of developing lymphoma.

The study, of nearly 1,400 adults with and without non-Hodgkin lymphoma

(NHL), found that those who were a first-born or only child were half as

likely to develop the cancer as people who were fourth in their line of

siblings.

In all, the researchers report in the Journal of the National Cancer

Institute, there was a linear increase in NHL risk, such that second-born

children had a lower risk than those who were third-born, who were, in turn,

less likely than later-born siblings to develop the disease.

Similarly, men and women who had had hay fever at any age were one-third

less likely than those without such nasal allergies to develop NHL, while

people with a history of food allergies were 70 percent less likely than the

food-allergy-free to be diagnosed with the disease.

NHL encompasses a group of cancers that arise in infection-fighting white

blood cells called lymphocytes. Little is known about the cause of these

lymphomas, though specific viruses do contribute to certain NHL subtypes

seen largely in Africa and Japan.

It's also known that people with immune deficiencies, such as HIV/AIDS, are

at heightened risk of developing the cancer. But whether other forms of

" immune dysregulation " are related to NHL risk is unknown, according to the

authors of the new study, led by Dr. E. Grulich of the University of

New South Wales in Sydney

To study the question, they looked at whether potential indicators of early

immune system development-such as allergies and birth order-were related to

NHL risk.

A number of studies have found evidence that limited exposure to infection

early in life may make a child more likely to develop allergies. The theory

is that this lack of germ exposure delays the normal " switch " that the

immune system goes through after birth to become an infection-fighting

machine. If the immune system is not given an early push in an

infection-fighting direction, it may tend to remain hypersensitive to

substances that most people tolerate -- which is what gives rise to

allergies.

Being an only child, or having otherwise limited exposure to other young

children, is one factor that can keep a person sheltered from germs early in

life.

So it's possible, according to Grulich's team, that elder siblings and only

children, as well as people with a history of certain allergies, are

partially protected from NHL by virtue of their immune responses.

The type of immune response associated with allergies is known as a

Th2-dominant response, as opposed to the Th1-dominant response that targets

foreign invaders like viruses. If the Th2-dominant response is indeed what

lowers NHL risk, Grulich and his colleagues write, the reason for the

benefit is unclear.

Further research, they conclude, is needed to confirm the associations found

in this study, and to better understand how the Th2 immune response might be

involved in NHL.

SOURCE: Journal of the National Cancer Institute, April 20, 2005.

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