Easton et al. BMC Public Health 2010, 10:459 http://www.biomedcentral.com/1471-2458/10/459 treatment [37] were also reported among patients with HIV/AIDS and lower health literacy. One study of 181 parents and caregivers found that those with lower health literacy lacked knowledge about weight-based dosing and this was associated with the use of nonstandardised medication dosing instruments [40]. Another study of 150 parents reported that low health literacy was associated with less parental asthma related knowledge, characterised by a two point differ- ence in a 20 point questionnaire [38]. A study of 600 pregnant women reported that those with lower reading levels had lower knowledge and less concern about the health effects of smoking on their unborn babies [30]. Other studies of 406 women in the community [43] and 505 female family planning clinic patients [22] found women with low health literacy were more likely to want to know more about birth control, [43] had lower knowledge of sexually transmitted infec- tions [22] and were less likely than those with adequate health literacy to know about fertile times within their menstrual cycle [22,43]. The 10 studies which found associations between knowledge of specific health issues and health literacy used 4 different measures and 8 different cut-off points for comparison, so although results suggest that knowl- edge is related to health literacy, (as would be expected, given the definition of health literacy), as with other relationships with health outcomes, it is unclear what aspects or levels of health literacy are most important. Two studies found no association between knowledge of health issues and health literacy score. One study found that among 543 parents, knowledge of their child’s diagnosis, medication name, purpose and instruc- tions for use was not associated with health literacy score [25]. In this particular study, parents with lower health literacy considered their child more sick for the same degree of illness compared with those with higher literacy and this may have had an impact on parental management of their child’s medication [25]. Another paper reported that among 400 women attending a family planning clinic, knowledge of contraception was generally poor, and although it tended to be better in those with higher health literacy, understanding of side effects of oral contraception and what to do about mul- tiple missed pills was not associated with health literacy [23]. It is unclear why this particular study differs from the others with a similar focus examined here. Two studies compared knowledge with related beha- viour. One found that knowledge did not mediate smok- ing behaviour among pregnant women. Those with higher health literacy had greater knowledge but the trend was towards higher smoking in this group although the relationship was not significant [30]. Another study reported that some beliefs about Page 7 of 10 medication did not mediate the relationship between health literacy and adherence and although beliefs about adherence norms were associated with adherence itself, this was independent of health literacy [37]. Emotional responses A further two studies focused on emotional responses of patients, either to their actual condition [29] or to sce- narios related to their condition [44]. Although emo- tional wellbeing can be considered as a contributory indicator of health status, we have reported these studies separately because it seems important not to obscure the possibility that the ‘outcomes’ they report might mediate other health status changes. Among 130 women at risk of developing cervical cancer, those with lower health literacy were more likely to have excessive levels of distress [29]. In a sample of 294 people living with HIV/AIDS, those with low health literacy had greater symptoms of affective depression but less evi- dence of negativistic thinking; they were more likely to endorse feelings of emotional distress, lower optimism and maladaptive coping when presented with a scenario of increased viral load [44]. Discussion The review has identified and summarised the reported associations between low functional or health literacy and health in the ‘hidden population’ of people with health literacy problems. It has also considered research relating to important moderators and mediators in the relationships between literacy and health, particularly health service use and self care behaviours. However, studies have not always considered the full range of fac- tors that may mediate or moderate the relationship between functional or health literacy and health, and some of the reported associations may obscure con- founding factors. As anticipated, there is evidence here that in the ‘hid- den population,’ low functional or health literacy is asso- ciated with poorer health status. These associations with poorer health may be mediated through differential use of services and access to good quality treatment. For example, the higher hospitalisation rates among those with lower health literacy [26] may suggest poorer self management, patients becoming more ill, presenting at a later stage to health services or waiting until they are in crisis before they contact services. In contrast to this, one study found no difference in uptake of preventive services related to health literacy level [25]. This may be because parents with low literacy may receive informa- tion about preventive health from additional sources or because they implement strategies to cope with and ensure they do not reveal their issues with literacy. For example, one of the questions in this particular study