Study authors say the risks rise for every kilogram a child weighs above the weight-for-age average.
"For each kilogram increase in birth weight there was a 44 percent increase in the risk that a child had food allergies or a 17 percent increase in the risk that they had eczema," Professor Kathy Gatford of Adelaide University's Robinson Research Institute told ScienceDaily.com.
This study was a meta-analysis, meaning it crunched data from multiple health record databases and other research efforts into fetal and birth weight as it relates to allergies. Researchers from the University of Adelaide examined more than 15,000 health records and dozens of other studies that included birth weight and allergy data. They used data from just 42 of these studies, but the total sample population comprises more than 2 million allergy sufferers.
What Causes Food Allergy?
Both heredity and environmental factors may play a role in the development of food allergy. The allergens in food are those ingredients responsible for inciting an allergic reaction, according to Melissa Conrad Stöppler, MD, MedicineNet author and editor. They are proteins that usually resist the heat of cooking, the acid in the stomach, and the intestinal digestive enzymes. As a result, the allergens survive to cross the gastrointestinal lining, enter the bloodstream causing (protein-induced) allergic reactions throughout the body. The mechanism of food allergy involves the immune system and heredity.
Immune system: An allergic reaction to food involves two components of the immune system. One component is a type of protein, an allergy antibody called immunoglobulin E (IgE), which circulates through the blood. The other is the mast cell, a specialized cell that stores up histamine and is found in all tissues of the body. The mast cell is particularly found in areas of the body that are typically involved in allergic reactions, including the nose and throat, lungs, skin, and gastrointestinal tract, Dr. Stöppler said.
Heredity: The tendency of an individual to produce IgE against something seemingly as innocuous as food appears to be inherited. Generally, people with allergies come from families in which allergies are common -- not necessarily to food but perhaps allergies to pollen, fur, feathers, or drugs. Thus, a person with two allergic parents is more likely to develop food allergies than someone with one allergic parent, Dr. Stöppler said.
How Does an Allergen Make You Sick?
Food allergy is a hypersensitivity reaction, meaning that before an allergic reaction to an allergen in food can occur, a person needs to have been exposed previously, or "sensitized," to the food. At the initial exposure, the allergen stimulates lymphocytes (specialized white blood cells) to produce the IgE antibody that is specific for the allergen. This IgE then is released and attaches to the surface of the mast cells in different tissues of the body. The next time the person eats that particular food, its allergen hones in on the specific IgE antibody on the surface of the mast cells and prompts the cells to release chemicals such as histamine. Depending upon the tissue in which they are released, these chemicals cause the various symptoms of food allergy, Dr. Stöppler said.