To all the stressed-out parents out there, here, let me just hand you a bit more to worry about. A research team led by Dr. Mary T. Caserta at the University of Rochester (more on her research here) have an article in press at Brain, Behavior, and Immunity entitled, ‘The associations between psychosocial stress and the frequency of illness, and innate and adaptive immune function in children’ (abstract here, unfortunately, I couldn’t find a downloadable version of the whole article). 169 school-aged children and their parents were studied through health diaries and over seven sequential visits, each separated by six months (three years total, by my quick calculation). At these visits, children were tested for human herpesvirus 6 reactivation and general measures of immune function were examined, such as ‘natural killer (NK) cell function and the percentage of CD4 and CD8 cells associated with immune control of cytomegalovirus (CMV).’

The study was to test the relation between parental stress and children’s immune systems:

Family processes have a substantial impact on children’s social and emotional well-being, but little is known about the effects of family stress on children’s physical health. To begin to identify potential links between family stress and health in children, we examined associations between specific aspects of family psychosocial stress and the frequency of illnesses in children, measures of innate and adaptive immune function, and human herpesvirus 6 (HHV-6) reactivation.

The researchers found that parental stress was associated with the illness rates in their children. Although HHV6 activation rates did not increase, the rate of illness in the children (according to the diaries, presumably) and the activation of the children’s immune systems were both elevated. It’s not entirely clear to me from the abstract, so I’ll have to wait for the full write-up to get a sense for the mechanisms involved. The researchers concluded, ‘There is an association between specific psychosocial stress exposure and rates of illness and immune function in normally developing children.’

The result is not entirely surprising, of course; we are more aware of psychoneuroimmunological dynamics, such as stress increasing one’s likelihood of getting sick and itself activating the immune system, and most people, I think, would assume that parental stress would likely cause stress — and stress-related adverse reactions — in their children. What I’m interested in more are the potential mechanisms involved in this social effect of stress. That is, how do the kids actually ‘catch’ stress and how does the stress-illness relationship exceed the boundaries of a single person’s body. Although I don’t know the immunological literature myself, I can think of a number of potential mechanisms.

First, there’s the most obvious one: stressed-out parents may interact with children differently in ways that would stress the children out. This one may not be terribly interesting to the neurosciences crowd, but it’s a simple social-psychological vector through which stress can be transmitted, and it’s entirely likely.

In addition, however, I can think of other more esoteric dynamics. For example, we’ve discussed mirror neurons, ‘chameleon effects,’ and other forms of motor-perceptual empathy. It’s also clear from a fair bit of this research that, even when we’re not consciously aware of it, we can ‘catch’ other people’s emotions by mirroring the subtle bodily cues of things like stress; I can imagine the speed of talking, posture, musculo-skeletal tension (shoulders, for example, in stress), facial expression, and a host of other subtle signs. If a child ‘mirrored’ these physiological facets of stress, it could induce stress in them.

Third, there may be less obvious ways in which stress is ‘communicated’ or contagious among people, such as phermones or chemicals on the skin. This could cause children’s immune problems by causing them stress, or these chemicals could have effects on the children’s bodies directly, without causing an intervening psychological state. For example, perhaps the parents’ phermones act on the children’s enteric nervous system (that which controls the intestines and digestion); the enteric system might have a stress reaction of some sort to these stimulants, possibly through the autonomic system, and this could lead to changes in digestion and gastrointestinal behavior. This may be preposterous — someone is welcome to comment on this — but the point is that there might be a mechanism distinct from any kind of mirroring or chameleon effects that wound cause parental stress to have effects on children’s immune systems or bodies.

Finally, there’s the other social-psychological dimension to this. From the abstract, I don’t know for sure how the research team controlled for reverse causation: maybe having a sick kid caused the parents to demonstrate higher levels of stress. Of course, this is pretty obvious, but it’s a less exotic, less interesting possibility that we might overlook simply because it’s not quite as much fun for the neuroanthropologists.

I suspect that there’s likely to be several of these processes operating at the same time; that is, parental care and subtle cues of stress might both be causing stress in the children. The effect might be compounding, cumulative, or non-cumulative — maybe there’s only so much stress that the kids can feel, so even if their parents don’t treat them any differently, the mirroring transference might be enough to cause the immunological effects in the children. That is, the demonstration of the effect doesn’t necessarily tell us how the cause works, and by implication, it doesn’t really tell us how we might try to apply this information to ameliorating the situation. For example, you might be able to create greater awareness of the issue in parents, which might increase guilt and ramp up the parental stress or telling them might allow them to monitor their own behavior, and thus maintain consistent caring behavior. We just don’t know from the effects of the stress how that stress is acting upon (or possibly, being acted upon by) the parent-child system. But at least one crucial principle is obvious; the boundaries of the body are not the absolute boundary of the physiological system within which stress and health interact.

References
Casertaa, Mary T., Thomas G. O’Connor, Peter A. Wyman, Hongyue Wang, Jan Moynihan, Wendi Cross, Xin Tu, and Xia Jin. In press (2008). The associations between psychosocial stress and the frequency of illness, and innate and adaptive immune function in children. Brain, Behavior, and Immunity doi:10.1016/j.bbi.2008.01.007