Autism and obesity, a confounder

The journal Pediatrics released a study recently claiming an association between autism and maternal obesity during pregnancy. As soon as I heard this study being splashed all over the media, I winced. As much as the journalists point out “correlation, not causation”, they also throw out vague warnings about obesity. On NPR this morning, the story was covered as being another casualty of the “rather striking epidemic of obesity”, and, in this article in the Washington Post, despite the lack of causation, the author warns “[s]ince more than one-third of U.S. women of child-bearing age are obese, the results are potentially worrisome and add yet another incentive for maintaining a normal weight, said researcher Paula Krakowiak, a study co-author and scientist at the University of California, Davis.”

Because, it’s all just our fault because of our behavior, right moms?

I don’t think so.

I was already pondering autism and causation recently. It has been an interest of mine for quite some time. Before I knew that I was going to go to medical school, when I got my first job at the first health food store, I was intrigued by the parents of children on the autism spectrum who would come into the store, desperately seeking anything to help. Many were trying gluten-free, casein-free diets, long before the recent gluten-free craze. Many were buying supplements. I was surprised at how many children on the autism spectrum there were. This was in the mid 90′s, and my first glimpse at the burgeoning numbers of children living with this diagnosis. I decided I wanted to work in the field, and help unravel this mystery for these parents.

Since then, my focus has obviously shifted. However, I have two cousin Susans with two sons each on the autism spectrum or with related developmental delays, which were also included along with autism in the study. One is closely related to my younger son’s father, and one is closely related to me. They are not related to each other at all. I know it is just anecdote, but I was already trying to look for a pattern – something they had in common. Why were their children affected, and mine not? I was overweight, possibly obese according to BMI, during both pregnancies. One of my cousins was, and one wasn’t.

Well, this study made things click in my head. There is a confounder strongly associated with obesity that was not looked at in the study. It is also associated with high circulating androgen levels, which have a known association with autism spectrum disorders. And, interestingly enough, both of my cousin Susans have this condition, and I don’t. It’s polycystic ovarian syndrome (PCOS). It is a lot less common than obesity, and would probably make more sense as a causation, both prevalence-wise, and physiology wise. I did a quick literature search, and couldn’t find anything on it.

I am not sure how difficult it would be to do a case-control study on this. It would be easy if I was at Kaiser. It was probably easier to look at weight and height at delivery than delve into gynecologic histories to find if there was any diagnosis of PCOS in the subjects of the study.

Well, trying to do some research on this is a definite possibility. Hopefully in the near future.

My big fat reading list

I keep on accumulating things I am reading that I wanted to talk about. Well, it has turned into a link fest. So, here’s my linkaround for the week, mostly journal club style:

Maternal Obesity and Breast-feeding Practices Among White and Black Women (pdf) and abstract. I had many problems with this article. First of all, the associations seemed really inconclusive. I would have preferred this data looked at through another lens, not obesity, but, since it was published in Obesity, I guess that was the point. The only association in any of the groups with BMI and breastfeeding was in the very obese, and that was only in white women. How is this an examination of race and BMI, except to show there WASN’T much of an association. I am also dismayed but not surprised at the higher cesarean rate among overweight and obese women. And, considering those higher cesarean rates, why did the adjusted hazard ratio NOT adjust for mode of delivery, when cesarean section has (in some research, not all) been associated with less initiation and success in breastfeeding? They adjusted for: mothers’ age, education, marital status at birth or during the pregnancy, Medicaid status, and pregnancy complications; parity; and first trimester initiation of prenatal care, but not mode of delivery.

What the data (not the discussion) highlighted was the racial disparity, not much about obesity and breastfeeding, and doesn’t offer much in the way of offering solutions or explanations as to why black women have such poorer rates of breastfeeding initiation.

Also from Obesity, BMI and Mortality: Results From a National Longitudinal Study of Canadian Adults.

Although a clear risk of mortality is associated with obesity, the risk of mortality associated with overweight is equivocal. The objective of this study is to estimate the relationship between BMI and all-cause mortality in a nationally representative sample of Canadian adults. A sample of 11,326 respondents aged ≥25 in the 1994/1995 National Population Health Survey (Canada) was studied using Cox proportional hazards models. A significant increased risk of mortality over the 12 years of follow-up was observed for underweight (BMI <18.5; relative risk (RR) = 1.73, P 35; RR = 1.36, P <0.05). Overweight (BMI 25 to <30) was associated with a significantly decreased risk of death (RR = 0.83, P 0.05). Our results are similar to those from other recent studies, confirming that underweight and obesity class II+ are clear risk factors for mortality, and showing that when compared to the acceptable BMI category, overweight appears to be protective against mortality. Obesity class I was not associated with an increased risk of mortality.

Emphasis mine. As someone in the obesity class I, I am feeling a lot of harumphing about this right now. I am waiting to hear all the criticism of underweight people (not that I would or I want it) from the peanut gallery, and the admission that overweight and mild obesity isn’t going to kill us all with the fat. I want a big fat apology to Dr. Regina Benjamin. (Commenting note: Please notice I never said appropriate exercise or a healthy-for-you diet were bad. That is not the topic. The topic is whether overweight and obesity deserves the constant, relentless public shaming and association with lack of health that it does).

And, just to be balanced, CNN has some information on why being overweight may negatively affect your health: provider bias. Yes, I also agree that some diagnostic tests and techniques like a manual pelvic exam or Leopold’s maneuver can be more difficult with more tissue there. But, the misdiagnosing and over testing (and over sectioning) of overweight and obese women is due to provider bias as much as testing and maneuvering fail. (Hat tip to Shakesville for that last one).