I teach first year medical students. And one of the things that we spend time on is how to analyze studies and whether or not the conclusions drawn are supported from the study. Which means the "devil is in the details". If you investigate the reports about this study, or listen to the interviews of the author, or the "experts" reporting on this study, the details that I am about to reveal have not been discussed. (At least I couldn't find them; I must admit I did not do an exhaustive literature search of other people's opinions.) And this is the meat of the matter.
This paper accepts the conclusions of existing research that shows associations of maternal employment with increases in children's BMI. Next, the authors look at data that was gathered for other reasons to support their hypothesis. But buried in their paper they state that children whose mothers changed their working conditions and schedules had higher BMIs than mothers who worked the entire time. They also found that if they looked at individual children they found these children had increased BMI, but not if they looked at groups of children of working women. The last important point is that they noticed the largest increased BMI if the mother started working when the child was in 6th grade. (They looked at the Home environment in 3rd and 5th grade, but not in 6th.)
Here are the problems that I find with this research:
1. This was a retrospective study. (They formed a hypothesis and found data that supported what they thought .)
2. Associations are not proofs. (There could be other things going on that caused the increase BMI that were the real etiologies.)
3. There were a lot of suggestions of why children of working mothers had higher BMIs, and many theories given; but no proofs.
4. They stated that studies "have linked maternal employment to children's weight, but the mechanisms that may mediate these associations remain largely unknown." (pg 69).
5. "(A)mong sixth graders, a mother's entry into employment was associated with an increase in BMI …and those children were about 6 times more likely to be overweight" and yet they did not have available a HOME score done in 6th grade (which measured the Home environment which assessed the "quality and quantity of support and stimulation provided to the child In his or her home environment". )
6. They did not record the children's Tanner Stage, which is a measure of a child's stage of going through puberty. (Pediatricians know that prior to a growth spurt children put on an extra layer of fat which temporarily increases the BMI. This is what you would expect around 6th grade. Girls go through puberty earlier before boys, and there are racial differences, so that could explain what is happening in sixth grade as the groups were not controlled.)
7. The people doing the study are not pediatricians. Although they all have PhDs, they are researchers and you get a different perspective when you are a clinician.
They did conclude 2 specific things:
1. It appears that the significant factor of BMI is the change in the maternal status of employment for the individual child and not whether or not the mother is employed. 2. A mother's entry into the work force at 6th grade seems to be most significant.
Here is what I take away from the study. There is definitely SOMETHING going on. I have always said that children are windows on a family. And another way to think about this study is that there is change going on in these individual families. When a parent changes her/his role in the family, it always effects the whole family (think about all the unemployment today and I wonder what a study that looked at the BMI of the children in these families would show us?)
And I think one of the most telling facts about the study is the large effect on the child if the mother enters the workforce in 6th grade. There is so much missing information from this study that I would assign this paper to my students to discuss what this paper does not tell us and have them discuss why they cannot draw the conclusions that they did.
What I can tell you from a pediatrician's perspective is 6th grade is an extremely stressful time for all children. They have major physical and hormonal changes, and if you add family changes to their social changes, I am not surprised to see that the biggest BMI change is at this time. My theory (which I think has as much validity as theirs, but is still a theory) is perhaps the mechanism is one of stress eating. Many of us do it. So instead of all of us feeling guilty and start our own stress eating, I would make some recommendations for stress reductions:
1. Do something fun with your child that is physical. (That will be the subject of some columns to come.)
2. . If you are going to stress eating, make sure it is the kind that will not add to your BMI.
There is also the idea that families with working mothers tend to be of lower socioeconomic status, as they can't afford to have one parent stay home. Thus, they are more likely to be unable to afford the kinds of food that would help keep BMI down. Working mothers are also a red herring--what if the father stays home? Do the children have higher BMI specifically because the mother is at work, or is just having a parent at home enough of a difference?
ReplyDeleteThis study culled data from The National Institute of Child Health and Human Development's Study of Early Child Care and Youth Development. There were only 979 children and families nationally from whom data were gathered. This data "contained fewer lower-income, minority, and single-parent families than in the general population". Also, this study did not look at whether or not the father worked. So, your points are well-taken and bring up more problems with this study and why all I conclude is that kids have higher BMIs these days and the etiologies are not clear.
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