Continuous farm life exposures protect children from hay fever

Hay fever was less common among children who lived on a farm and consumed unprocessed cow’s milk than among other children in rural areas, according to a study in The Journal of Allergy, Asthma and Clinical Immunology: In Practice.

But this milk was only protective when exposure was consistent and not just early or later in life, Sonali Pechlivanis, PhD, lecturer at the Institute of Asthma and Allergy Prevention, Helmholtz Zentrum Munchen, German Research Center for Environmental Health, Neuherberg, Germany, and colleagues wrote.

Researchers assessed 769 children (47.7% girls) from the Protection Against Allergy Study in Rural Environments birth cohort, including 367 (47.7%) children who were born to mothers who lived on family-run livestock farms at the time of birth.

At age 10.5 years, 12.9% of the children had hay fever.

The children who grew up on a farm had half the risk for hay fever as those children who did not grow up on a farm (adjusted OR = 0.5; 95% CI, 0.31-0.79).

When the researchers assessed the extent of exposure to animal sheds among these children, they found those with only early exposure had a statistically insignificant reduced risk for hay fever compared with those with no exposure (aOR = 0.26; 95% CI, 0.06-1.15).

Children with continuous consumption of farm milk had a significantly reduced risk for hay fever compared with those with no consumption (aOR = 0.35; 95% CI, 0.17-0.72), but this effect did not persist among children with only early consumption.

dAlso, those with the highest quintiles of farm milk consumption showed a greater protective effect than those with the lowest consumption (aOR = 0.37; 95% CI, 0.16-0.84).

But, the protective effect of farm milk appeared attenuated when children also drank processed milk (aOR = 0.43; 95% CI, 0.19-0.96). In fact, the researchers found that daily consumption of “shop” milk at age 10.5 years was positively associated with hay fever.

When evaluating the effect of the early-life microbiome, researchers found an inverse association between hay fever and the bacterial richness of the gut microbiome at age 12 months (aOR = 0.66; 95% CI, 0.46-0.96).

During the first year of life, farm milk consumption (adjusted geometric mean ratio [aGMR] = 1.2; 95% CI, 1.03-1.4) and exposure to animal sheds (aGMR = 1.19; 95% CI, 1.01-1.4) increased gut microbiome richness.

In fact, researchers found that gut microbiome richness provided 18.4% of the total protective effect of farm milk consumption and exposure to animal sheds in the first year on hay fever (P = .03).

Although gut microbiome richness at age 12 months and animal shed exposure through age 3 years were determinants of hay fever, the researchers wrote, continuous farm milk consumption from infancy through school age was necessary for a protective effect.

The researchers concluded that their findings do not support notions that early exposures in the first months of life alone would govern later outcomes and that, instead, continuous exposure is necessary for protection.