Heavy Babies More Likely to Develop Rheumatoid Arthritis

Heavy babies could be more than twice as likely to develop rheumatoid arthritis than babies of a normal weight according to an American study published this month in the journal Annals of the Rheumatic Diseases.

The study focused on 13,639 women from the Nurses Health Study who were followed between 1976 and 2002. During that time 683 (5.0%) of the women developed rheumatoid arthritis. The researchers found that women with a birth weight greater than 10 pounds (4.54 kg) were 2.1 times more likely to develop rheumatoid arthritis later in life than women with a normal birth weight between 7 and 8.5 pounds (3.2 to 3.85 kg). The results persisted even after adjustment for potential confounders such as mothers socio-economic status, parental smoking, and maternal diabetes.

While the mechanism which links heavy babies to rheumatoid arthritis is unknown, researchers believe that hormone imbalances observed in rheumatoid arthritis sufferers may be “programmed” during early fetal development.

The study adds support to the idea that the probability of developing certain diseases may be influenced by processes that occur during pregnancy, a theory known as the “fetal origins of adult disease hypothesis”. A low birth-weight for example has been linked to an increased risk of heart disease, strokes, childhood asthma, and type-2 diabetes while a very high birth-weight has been linked to certain cancers such as leukemia, colo-rectal, ovarian, prostate, and breast cancer.

Another possible explanation for the link lies in the fact that very heavy babies are more likely to become obese later in life. The risk of developing rheumatoid arthritis is around 50% higher in obese individuals compared to the general population.

Interestingly, while the average weight of an American adult has steadily increased over the last 50 years, the average weight of infants at birth has actually decreased slightly. In 1995, the average infant weighed 3.35 kg compared to 3.32 kg in 2008. This is likely due to an increasing percentage of babies born to women aged over 45 (very young and very old mothers are more likely to give birth to underweight babies).