Summary of findings

For the first time, this systematic review summarises current evidence on risk for poor physical health in offspring of parents with mental disorder. Overall, this detailed evidence synthesis paints a picture of relatively poor physical health in the children of parents with mental disorder, with pooled effect estimates revealing an increased risk of injuries, asthma, malnutrition and diarrhoea. However, we highlight striking gaps in the evidence: over three-quarters of the studies focused exclusively on maternal depression and, of those, half on postnatal depression; there is little information about children of parents with mental disorders other than depression or anxiety; and few studies investigated the impact of paternal mental disorder.

In total, 63% of studies (26/41) reported an effect of parental mental disorder on physical health outcomes in the offspring. A further 17% of studies (7/41) estimated a positive association, albeit with 95% confidence intervals that include a null effect. Most of the identified studies examined the relationship between exposure to parental mental illness (predominantly maternal postnatal depression) and risk of childhood injuries (n = 10), obesity (n = 10) or asthma (n = 8). Of note, no eligible studies assessed risk of childhood cancers, diabetes, epilepsy or migraine and only one assessed the impact of serious mental disorders such as schizophrenia or bipolar disorder on childhood physical health. Similarly, no studies assessed effects of dual diagnosis, maternal or paternal personality disorder or eating disorders.

Research in context

We identified evidence of an increased risk of childhood accidents or injuries associated with parental mental illness (OR_pool = 1.15, 95% CI 1.04–1.26).^{Reference Phelan, Khoury, Atherton and Kahn27–Reference Raitasalo and Holmila35} Self-reported data have shown that periods of depression affect a mother's ability to supervise her child.^{Reference Phelan, Morrongiello, Khoury, Xu, Liddy and Lanphear68} Substance misuse, particularly alcohol dependence, is associated with violent behaviour,^{Reference Cleaver, Nicholson, Tarr and Cleaver69} which may confer additional risk of injury to the child. The one study that examined the effect of psychosis on risk of childhood accidents did not find an effect, although the confidence intervals indicate that it was underpowered to detect less than a doubling in the rate of accidents.^{Reference Howard, Goss, Leese and Thornicroft36} All but two of these studies on accident and injury followed children in the first 6 years of life and therefore we do not know whether the risk is ameliorated by school entrance.

We highlight evidence to of an increased risk of childhood asthma associated with parental mental illness (OR_pool = 1.26, 95% CI 1.12–1.26) and some evidence to suggest an increased risk of other atopic disorders (OR_pool = 1.36, 95% CI 0.91–2.03). The association was observed most strongly in studies in which the exposure was categorised as severe^{Reference Cookson, Granell, Joinson, Ben-Shlomo and Henderson37} or chronic.^{Reference Brew, Lundholm, Viktorin, Lichtenstein, Larsson and Almqvist40,Reference Wang, Wen, Chiang, Lin and Guo45} Prior research has reported psychosis and atopic disorders clustering in individuals^{Reference Chen, Lee and Lin70,Reference Pedersen, Benros, Agerbo, Børglum and Mortensen71} and families.^{Reference Pedersen, Benros, Agerbo, Børglum and Mortensen71} The familial link between mental and atopic disorders could arise as a result of shared aetiological factors but also as a result of the effects of adversity. Parental mental disorder increases risks for a range of adversities during childhood, such as poverty^{Reference Fitzsimons, Goodman, Kelly and Smith72,Reference Wickham, Whitehead, Taylor-Robinson and Barr73} and trauma.^{Reference Björkenstam, Kosidou and Björkenstam74} Exposure to adversity and stress can alter a child's immune response,^{Reference Fagundes and Kiecolt-glaser75} which in turn increases the risk for atopy.^{Reference Sternthal, Enlow, Cohen, Canner, Staudenmayer and Tsang76} Yet, the link between mental disorders and atopy is likely complex and might include combinations of direct and indirect effects of parental disorder, as well as shared environmental factors (such as smoking).

The evidence for a link between parental mental illness and childhood overweight or obesity is inconclusive. Prior reviews that included cross-sectional studies did report a correlation between maternal depression or anxiety and childhood obesity;^{Reference Milgrom, Skouteris, Worotniuk, Henwood and Bruce19,Reference Benton, Skouteris and Hayden21} another that included only prospective designs found a link with chronic, but not with episodic (mostly postnatal), maternal depression.^{Reference Lampard, Franckle and Davison20} All of the studies we identified that investigated this relationship used prospective cohort or case–control designs, which generally had smaller samples than studies that used registry-based cohorts. Therefore, the lack of definitive findings may be due to lack of power of individual studies.

All the studies from LMICs reported a positive association between maternal depression and offspring malnutrition or diarrhoea. Half of these exclusively examined the effect of postnatal depression in the first year after birth. Recent reviews have reported rates of maternal postnatal depression in LMICs of around 20%,^{Reference Fisher, Cabral de Mello, Patel, Rahman, Tran and Holton77} considerably higher than the 6.5–12.9% seen in affluent Western populations.^{Reference Gavin, Gaynes, Lohr, Meltzer-Brody, Gartlehner and Swinson78} Evidence also suggests that maternal mental ill health is associated with both poor fetal and child growth.^{Reference Gelaye, Rondon, Araya and Williams79,Reference Surkan, Kennedy, Hurley and Black80} Therefore, maternal mental health has been highlighted as a priority target for screening mothers in these settings.^{Reference Walker, Wachs, Meeks Gardner, Lozoff, Wasserman and Pollitt81}

Strengths and limitations

The review highlights how children of parents with mental illness have multiple physical health challenges, on top of previously identified mortality^{Reference Webb, Abel, Pickles and Appleby13,Reference King-Hele, Webb, Mortensen, Appleby, Pickles and Abel85} and neurodevelopmental risks.^{Reference Rasic, Hajek, Alda and Uher7,Reference Stein, Pearson, Goodman, Rapa, Rahman and McCallum86} Several strengths of our review reinforce the findings. First, although the different outcomes under consideration preclude direct comparison of estimates, there is general consistency in the effect sizes estimated, lending weight to the evidence. Also, we use strict definitions of study design; this means that the estimates are better approximations of effect sizes than if weaker study designs were used: i.e. cross-sectional studies. Therefore, we indicate where potential mechanistic explanations should be explored, so that modifiable factors might be identified to help this vulnerable group. The included studies come from heterogeneous samples, countries, settings, measures and designs. This strengthens the conclusions of the review because, as the results generally show consistency, we can assume that the findings are independent of these factors.

To date, this is the most comprehensive review and meta-analysis of the associations between parental mental illness and offspring physical illness during childhood, however there are a number of limitations. Few studies investigated the effect of both maternal and paternal mental illness and, generally, they noted weaker effects for paternal exposure.^{Reference Howard, Goss, Leese and Thornicroft36,Reference Magnus, Wright, Røysamb, Parr, Karlstad and Page41,Reference Klinnert, Nelson, Price, Adinoff, Leung and Mrazek42,Reference Wang, Anderson, Dalton, Wu, Liu and Zheng53} This indicates that maternal condition plays a more important role in the risk of offspring physical ill health, either as a result of intrauterine exposures, or through early childhood experiences or both; it also provides some evidence against a purely genetic cause for these relationships.

All the identified studies come from observational settings and are therefore subject to confounding bias. Most attempted to account for this bias, primarily using regression adjustment. Notably, most of the adjusted analyses were closer to a null effect size. This indicates that, overall, factors that increase the risk of parental mental illness are also likely to increase the risk of poor physical health in offspring (and vice versa). One obvious candidate for a variable of this kind is socioeconomic or multiple deprivation, inextricably linked with parental mental ill health^{Reference Elliott82} and poor child physical health.^{Reference Rough, Goldblatt, Marmot, Nathanson, Mansfield, Foyle and Nathanson18,Reference Bradley and Corwyn83}

Despite adjustment for confounders, we must be cautious before attributing the causes of poor child physical health to parental mental disorders. First, not all the potential confounders are likely to be identified and measured in data available to researchers. Two of the more recent studies tried to account for residual confounding from familial factors by investigating whether associations still persist using sibling or cousin analysis^{Reference Brew, Lundholm, Viktorin, Lichtenstein, Larsson and Almqvist40,Reference Magnus, Wright, Røysamb, Parr, Karlstad and Page41} or when investigating paternal exposure.^{Reference Brew, Lundholm, Viktorin, Lichtenstein, Larsson and Almqvist40} Second, some studies may be subject to overadjustment, where analyses adjust for variables on the pathway between the exposure and the outcome. For example, poor fetal growth is associated with both prenatal maternal mental disorder^{Reference Lewis, Austin and Galbally84} as well as many health outcomes. Therefore, this might be the mechanism by which prenatal maternal mental disorder influences child health and studies that adjust for this might be underestimating the effect of maternal mental illness on child health. Third, although we excluded studies in which it was clear that the outcome was measured before the exposure occurred, for many studies this was unclear. Therefore, we cannot rule out that at least some portion of the results were because poor child health affects parental mental illness and not vice versa. Fourth, although we actively tried to include unpublished research, all the identified studies were from the published literature. Therefore, it might well be that some positive findings are the result of publication bias.

Implications for future research and policy

This systematic review shines a stark light on the gaps in our knowledge about the physical health of children whose parents have mental illness, and highlights a need to shift the focus of research towards parental mental disorders other than maternal postnatal depression. Future studies should interrogate the extent to which antenatal, perinatal and postnatal exposures have differential effects on offspring's risk of physical illness. Also, maternal mental disorder may pose more risk to child physical health than paternal disorder but there is a strong need for future studies to include paternal exposure where possible if we are to understand the mechanisms behind these effects in particular outcomes. This chimes well with recent calls for research and policy to place a greater emphasis on the role of fathers in children's lives.^{Reference Clapton87}

Future research should interrogate the associations highlighted here to explore behavioural, environmental and genetic causes. To do this we highlight a need to develop fresh approaches to understanding the links between child physical health and parental mental health. These include the necessity of accounting for key confounders and to consider the use of alternative design strategies, including negative controls, sibling or quasi-experimental designs.^{Reference Lawlor, Tilling and Smith88} If future research is to be able to deepen our understanding of when and how these vulnerable children are at risk of preventable illnesses, large high-quality cohorts must be identified. For example, to investigate mechanisms of childhood asthma (still the most common childhood illness) we need to look at effects of different parental illnesses and effects of maternal versus paternal mental disorder. Combining data across such cohorts from different countries may offer such an opportunity.

Finally, from a policy perspective, such approaches can offer the detail needed to plan resource allocation and develop new service provision. Studies describing patterns of healthcare utilisation by these children and parents may be particularly valuable for this.