This week, Dr. Sydney Spiesel discusses a new and rigorous study on the impact of breast-feeding, physical and psychological; the effect of bad marriages on the health of the heart; and a paradoxical finding about cod-liver oil.
Breast-feeding: How good for babies is it really?
Question: How do you establish the benefits of breast-feeding in a scientific way? It would be unethical—and, of course, impossible—to assign mothers randomly to either breast-feed their infants, say exclusively for six months, or to give them formula. But the differences between mothers who breast-feed exclusively and mothers who don't include socioeconomic status, degree of education, employment, ethnicity, and a host of other factors. And so without running a randomized trial, it's extremely difficult to know what's causing any perceived difference between the two groups of babies. Is it the feeding choice or some other difference in the mothers that plays the central role?
New study: Despite the obstacles, one research team headed by Dr. Michael Kramer of McGill University in Montreal has devised a rigorous approach. Instead of randomly assigning individual women to breast-feed or formula feed, this research group promoted breast-feeding in some arbitrarily chosen geographic areas around maternity hospitals in Belarus, leading to much higher rates and duration of breast-feeding. The authors then compared the women and babies from these areas with women and babies in areas where maternity centers just continued whatever had been their customary practice, having isolated the effect of an increased breast-feeding rate.
Physical findings: Dr. Kramer's group previously found some medical benefit to breast-feeding, though less than I expected. (As I have said before, I am a proponent of breast-feeding.) Increased breast-feeding reduced the rate at which babies developed diarrhea or eczema but, contrary to expectations, had little or no effect on respiratory disease.
Psychological findings: The recently reported bigger surprise, however, was that increased breast-feeding appeared to make no difference on the psychological front for babies or mothers. About 14,000 children, from the two groups, were examined when they were 6½ years old for problems with conduct, hyperactivity, and peer relations. The researchers also looked at mothers' satisfaction with their marriages and in their relationships with their children. To my amazement, the study turned up no differences in any of these outcomes. I was sure that, on average, the tactile nature of breast-feeding would promote mother-child closeness, which would mean better adjustment for the child and greater satisfaction for the mother. I was wrong.
Conclusion: Which puts me in a very awkward position. Breast-feeding is a topic that evokes strong feelings, and merely presenting facts that might be taken as not fully supportive makes some people angry. Very angry. Breast-feeding is clearly critical—and even life-saving—in parts of the world that lack sanitation and access to fresh water and refrigeration. I continue to believe that there is a biological benefit to breast-feeding even in the developed world, where the risks of formula feeding are fewer. But I am now less sure of the psychological benefit to mother or child. Finally, I still believe that the baby will prosper most if the mother's choice of feeding method is the one that gives her the most satisfaction and pleasure. But now I want that question to be scientifically studied, also.
Marital bliss: Does it make the heart healthier?
Question: Epidemiologic research has shown that social relationships can protect adults from risk of illness and death, and that marriage is particularly beneficial. But what about bad marriages? Is it better to be single than to be in one?
New study: Recent research begins to shed light on this long-ignored question. Dr. Julianne Holt-Lunstad and colleagues used blood pressure as a marker for cardiovascular risk and studied about 300 adults who responded to an ad. Two-thirds of them were married and one-third were single. Blood pressure, measured frequently over a 24-hour day, was used as a rough index of cardiovascular health.
Findings: The authors found that marriage clearly promotes healthier blood-pressure levels, but only for married people who scored high for marriage quality, as reflected by their lower levels of stress, less depression, and higher satisfaction with life. Unhappy married people had poorer blood-pressure levels than the single people included in this study. Interestingly, the benefits of a supportive network didn't protect either single people or unhappily married people from blood-pressure problems, which suggests that there is something special about the marriage relationship.
Caveat: This is a preliminary study with many weaknesses. The sample is small, and the participants were not randomly selected—they chose to be studied. The participants were all white and mostly educated. The couples were all legally married and heterosexual. This self-selected group may or may not resemble the general population in ways that affect their answers to the authors' questions. Also, we don't know whether measuring blood pressure during a single day means anything about future rates of cardiovascular problems.
Conclusion: Nevertheless, the finding is worth following up. It is easy to imagine a health benefit that might be attributable to, let's say, a higher likelihood of regular meals or shared warmth at night, or less need for risky sex. But the benefit might come from somewhere else—like the diminished stress associated with a satisfying relationship. Maybe marital bliss really is good for the heart.
The mysteriesof cod-liver oil
New study: Perhaps unjustly, I tend to think of studies with unexpected findings as the most reliable, because results contrary to a researcher's expectations would seem less likely to be the result of unconscious error. So I was immediately drawn to a recent study from Norway of 3,000 women, ages 50 to 70. It reported lower bone density for women who drank cod-liver oil in childhood than for women who escaped this treatment.
Treatment: Cod-liver oil, which I remember with a shudder from my own childhood, is a vitamin-rich liquid, indeed manufactured from fish livers. It's still widely used in Norway and Sweden to prevent vitamin-D deficiency (and build character) in children. In parts of the world with plenty of bright sunlight, our bodies naturally produce this vitamin, which we need to incorporate calcium into the bones. But in cold and dark regions, a daily teaspoonful of cod-liver oil is often downed as a substitute. The makers of modern-day versions claim they are free of the offensive taste and odor I remember.
Findings: When children don't get enough vitamin D, the result is poor incorporation of calcium into the bones, which, later in life, leads to poor bone density. This likely accounts for the great frequency of bone fractures observed in elderly Scandinavians. It seems obvious, then, that women who drank cod-liver oil in childhood would have better bones than women who didn't. And yet these authors found that the opposite—the cod-liver group actually had less calcium in their bones than the other women.
Explanation: How to make sense of this paradox? The most likely cause is an interesting one: too much of a good thing. In addition to vitamin D, a teaspoon of cod-liver oil contains too much vitamin A. (Or at least it did until a few years ago, when manufacturers reduced the vitamin-A level in cod-liver oil to a safe level.) Now, vitamin A is wonderful stuff, too: People who don't get enough of it suffer poor vision and eye damage and are at great risk for serious consequences if they develop infectious diseases like diarrhea and measles. But take in too much of this vitamin, and the effects range from liver damage to nervous-system symptoms that resemble the effects of a brain tumor. And excessive vitamin A is associated with bone mineral loss, leading to osteoporosis late in life and a high risk of hip fractures in the elderly.
Conclusion: It seems most likely that the good the vitamin D in cod-liver oil did for bones was more than reversed by the bad done by too much vitamin A in the old product. We'll know soon enough if that theory is right: We just need to see if elderly Scandinavians break fewer bones now that cod-liver oil gets the vitamin-A dose right.