Do formula-fed children face increased risk of leukemia?
This news release summarizes a published report on data from 18 separate studies worldwide that, when analyzed together, suggest breastfeeding is associated with reduced risk of developing childhood or adolescent leukemia. But that’s basically the only message conveyed by the news release, which is otherwise devoid of important context, including — most importantly — on the limitations of the observational design used by all of studies in the analysis. The release’s incomplete, one-sided presentation will most likely lead to a flurry of overblown media coverage that could have negative repercussions for the many women who cannot or choose not to breastfeed.
There are many reasons for women to think that breastfeeding is a good choice for their babies. Is leukemia prevention one of them? That’s the suggestion of the study reported on here, which is a re-analysis of previous studies examining the question. It’s worthwhile research, but let’s remember that these underlying studies all relied on a backward-looking case-control design that is subject to selection bias and a variety of other potential problems. And the scope of the potential benefit for this condition, which is thankfully quite rare, is limited. Our worry here is that women face a number of physical and lifestyle constraints that may affect their ability to breastfeed. And women who can’t breastfeed already experience guilt that they aren’t doing enough for their babies. Should they also be made to feel as if they are putting their children at increased risk of cancer? That’s not a justifiable message based on this study. But without more careful communication of study limitations and other context, we’re afraid that that’s the message that could ultimately reach the public.
While it’s obvious that breastfeeding is free of charge, readers might not appreciate what an advantage this is compared with prepared formulas. This is an especially important consideration in the developing world where a desire for westernization has caused a significant bump in infant formula sales. The average annual cost of a brand-name infant formula is approximately $1200 in the US. Then again, there’s potentially a cost to breastfeeding in terms of work/career advancement for the mother and the labor value of time spent breastfeeding/pumping. Breast pumps can be expensive, too. The news release didn’t need to explore all of this, but some acknowledgment of the issues at play would have been welcome.
According to the release, this analysis of 18 studies found that “breastfeeding for six months or longer was associated with a 19 percent lower risk compared with no breastfeeding or breastfeeding for a shorter period of time.” A sub-analysis of 15 studies further showed that “ever being breastfeed” for a shorter period of time was associated with an 11 percent lower risk in developing leukemia compared to those who were never breastfed. But how big really is a “19% lower risk”? That depends upon whether leukemia is generally common or rare. A 19% reduction in a rare condition like childhood leukemia won’t amount to a very large absolute benefit. The release could have put a number on it.
We’re on the fence here. We’re not suggesting that breastfeeding causes serious harm to mother or child, except perhaps in some cases of infectious disease transmission. However, breastfeeding isn’t always the peaceful scene of contentedly suckling infant often portrayed in the media. Cracked nipples, nipple pain, engorgement, mastitis (breast infections) are not uncommon and can reduce breastfeeding success. In addition, breast milk is low in vitamin D, and exclusive breastfeeding may increase the risk of rickets. Some acknowledgment of these issues could potentially encourage steps to prevent and address these problems, which would be beneficial.
This was a meta-analysis of observational studies of breastfeeding and leukemia risk. As we’re often fond of saying, these types of studies are incapable of proving cause and effect. And yet the release is headlined, “Study Suggests Breastfeeding May Lower Risk of Childhood Leukemia” — the clear implication being that breastfeeding may have “caused” the reduction in leukemia. The release also fails to mention any weaknesses or limitations in the study design. This is important, because case-control studies sit near the bottom of the evidence pyramid and their findings should be viewed cautiously. And this study doesn’t control for confounding factors that could affect leukemia risk. The weaknesses that were cataloged in the original study (but not the release) include the following: the voluntary responses from mothers were collected in most of the studies years after the time of breast-feeding which might affect accurate recall; the response rates varied from 47 percent to 98 percent in the leukemia cases in a majority of the studies; and the response rates from controls were believed to be skewed toward a higher response rate from people with a higher socioeconomic status (which itself might be associated with lower rates of leukemia). Further, and perhaps most importantly, some studies didn’t define whether the breastfeeding was exclusive or if the babies were concurrently fed with formula or other foods.
The news release also doesn’t define how many children were followed and for how long. This is an unfortunate oversight since the size, length and global nature of the study are its strong points. According to the research paper published in JAMA Pediatrics upon which the release is based, data from 10,292 leukemia cases and 17,517 controls were analyzed. Many of the studies followed children from 0 years to 14 years, some longer. The analysis includes 18 studies published over a 54-year period in 13 developed countries and five lesser developed countries. While the findings must still be viewed cautiously, the depth of data analyzed lends it more credence than research involving a small sample size and a brief time frame.
The release states that “Leukemia is the most common childhood cancer and accounts for about 30 percent of all childhood cancers.” And it suggests that breastfeeding can prevent these leukemias, which has the potential to make mothers feel badly if they’re unable to successfully breastfeed (a common phenomenon). But the release never provides the comforting information that cancer in children is, according to the National Cancer Institute, a “rare” disease. This is important context.
Neither the news release nor the study cited any outside sponsors. The study was completed by epidemiologists at the School of Public Health in Haifa, Israel, and the Ministry of Health in Ramat Gan, Israel.
Perhaps it goes without saying that the alternative to breast milk is infant formula, but the release could have stated this explicitly, which would have provided an opportunity to point out the other potential health advantages of breastmilk as well as the financial advantages. Not doing so provides a rather incomplete narrative.
While it may be assumed that breastfeeding is available to all, this is an oversimplification. Many women have trouble initiating breastfeeding and may have jobs or other limitations that make it difficult to breastfeed. The public can be hostile to breastfeeding women. Some women do not produce enough milk to exclusively breastfeed their babies. Studies have found that while about 75% of women attempt to breastfeed in the first week, only about 30% are still exclusively breastfeeding by three months. Some acknowledgment of the difficulties involved would have provided an opportunity to mention programs and interventions, including postpartum skin-to-skin contact, partner education, lactation consultants, etc, that may improve breastfeeding success.
The news release did not comment on the novelty of the research, and doesn’t tell us how this study differs from other meta-analyses of studies of breastfeeding and childhood leukemia. As the study authors claimed in the published report, “to our knowledge, this is significantly the largest and most up-to-date review and analysis of current knowledge on childhood leukemia and breastfeeding.”
While the suggestion that breastfeeding reduces leukemia rates is questionable, we’ve already flagged the release for that concern. The release makes no other unwarranted claims and its tone is generally measured.
Systematic, Criteria-Driven
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