Birth weight associated with AF risk
BOSTON, MASSACHUSETTS. It is well established that a low birth weight is associated with an increased risk of developing heart disease and diabetes. Now a group of researchers from Brigham and Women's Hospital, Harvard Medical School and the University Hospital, Basel, Switzerland report that a high birth weight is associated with an increased risk of developing atrial fibrillation (AF) later in life.

Their study involved 27,982 white, female health professionals who were over 45 years old at enrolment in 1993. They were all free of heart disease and AF at baseline. During an average follow-up of 14.5 years, 735 women (2.6%) developed AF. The researchers observed a clear relation between birth weight and AF. Women with a birth weight of 2.5 kg (5 lb 8 oz) or less had an age-adjusted incidence of 1.45 per 1000 person-years of follow-up, while women with a birth weight greater than 3.9 kg (8 lb 10 oz) had an age-adjusted incidence of 2.56 per 1000 person-years.

Thus women with a high birth weight had a 75% greater risk of developing afib than did those with a low birth weight. This association persisted even after adjusting for such confounding variables as cholesterol level, smoking, physical activity level, alcohol consumption, level of education, race, hormone replacement therapy, body mass index (BMI), blood pressure, and the presence of diabetes.

However, when adjusted for adult height and maximum body weight between the ages of 18 and 30 years, the relationship between birth weight and AF risk was no longer statistically significant. The authors speculate that this may be because birth weight is an important determinant of adult height and body size. They conclude that birth weight is significantly associated with the risk of developing afib suggesting that early life determinants may play an important role in the pathogenesis of atrial fibrillation. They also suggest that the increasing number of newborns with elevated birth weight may be partly responsible for the increasing incidence of AF in the general population.

Conen, D, et al. Birth weight is a significant risk factor for incident atrial fibrillation. Circulation, Vol. 122, August 24, 2010, pp. 764-70
Frost, K and Olsen, J. Birth weight and atrial fibrillation – a causal link? Circulation, Vol. 122, August 24, 2010, pp. 759-60

Editor's comment: An association between elevated birth weight and atrial fibrillation was first reported in LAF Survey 14 carried out in 2007. The survey found that afibbers who were able to control their afib (Group A) had a median birth weight of 3.28 kg (7 lb 3 oz), while those whose condition worsened (Group B) had a median birth weight of 3.7 kg (8 lb 2 oz). Patrick Chambers, MD, a frequent poster in the early days of the Bulletin Board, followed up on this and other findings in an additional survey LAF vs. AF which was discussed extensively on the Bulletin Board. Based on his findings he wrote the article "Lone Atrial Fibrillation: Pathologic or Not?" which was published in Medical Hypotheses and further discussed in Conference Room Session 55.

Dr. Chambers concluded that lone and heart disease-related AF can be distinguished based on weight, height, hip and waist measurements. In relation to the birth weight finding in LAF Survey 14, he pointed out that a higher birth weight such as found in Group B is associated with increased baroreflex sensitivity[1] and that an increased baroreflex sensitivity, in turn, is associated with more difficulty in dealing with sudden changes in autonomic tone that could lead to an afib episode. Thus, it may well be that lone afibbers can be divided into two groups - those (like in Group A) whose main underlying problems are magnesium deficiency, wheat sensitivity, etc. and those (like in Group B) whose main underlying problem is an increased baroreflex sensitivity. Clearly, it would be much easier to correct a magnesium deficiency than an increased baroreflex sensitivity, perhaps explaining why "nothing worked" for Group B. It is also intriguing to speculate that the reason why mixed type afibbers (neither pure adrenergic nor pure vagal) have a more difficult time reducing their afib burden could be that they have increased baroreflex sensitivity. Hopefully, medical researchers will some day cast more light on this finding.

[1] Leotta, G, et al. Effects of birth weight on spontaneous baroreflex sensitivity in adult life. Nutrition, Metabolism and Cardiovascular Diseases, Vol. 17, May 2007, pp. 303-10