Self-reported mental health generally improves by early old age, but social class differences in anxiety and depression increase with age . In the Whitehall II study, social inequalities in both self-reported mental health and general health increased in early old age, as the rate of improvement in mental health was less for those in the lower employment grades . Using a framework derived from the social determinants of health, we summarise the direct and indirect impact of housing patterns on health inequalities . We then analyse the specific roles of housing tenure and quality, as well as financial security over the life course, in explaining the pattern of improving mental health, but increasing mental health inequalities in the Whitehall II Study. We conclude by discussing which public policies could reduce mental health inequalities in older people.
Housing patterns and health inequalities
Studies of patterns of health inequalities in older age groups are primarily focused on 'lifestyle' rather than structural variables and largely ignore possible explanatory variables such as housing, despite strong evidence linking housing tenure to adult health in various longitudinal [5, 6] and cohort studies [7, 8]. Housing costs, including fuel use, rent or mortgages, maintenance and repairs, are a significant component of the minimum income for healthy living required by older people  and those who are home-owners may be mortgage-free by the time they retire. Time-use surveys consistently show that older people spend more than 90% of their time indoors, mostly in their homes,  so that the indoor home environment is their most significant environmental exposure, as well as being the place that they have most contact with their families or friends.
Generally, housing affects people's health at several levels . Housing tenure is a structural variable; houses are usually the largest capital asset owned by families and this wealth can be used to generate a stream of income, in addition to salary, wages and benefits. In Britain, wealth is highest for those close to retirement, but inequalities are pronounced and magnified by differential access to pensions [12, 13].
Those who rent, whether from a private landlord or a social housing agency, are likely to be poorer, although in some cases they may be trading off more income for less wealth . There is also a possible cultural effect of tenure choices on mental health. In England, people generally aspire to home ownership and renting is seen as a temporary measure. Renting permanently is more unusual, or may be seen as a sign of failure (particularly renting in the public sector). However, in some European countries, renting is just another housing option. Nonetheless, there is cross-cultural evidence that people who own their own houses are in better health than people who rent their houses, even controlling for income .
Home-ownership seems to confer both psychological and material advantages on owner occupants, [16–18] although a recent systematic review concludes the evidence is not strong . Psychologically, owning a home rather than renting seems to confer greater autonomy and social status ; what economists call 'positional goods'. Houses that are owned are generally in better condition than rented accommodation. Rental housing is generally of poorer quality and more insecure. Leases, though they vary from country to country, do not give the same security to tenants as a house title gives to an owner . However, this is not a static situation, in part because the housing market is such a pivotal part of the general economy and in an economic recession, home-owners, who bought in a boom, may be left with negative equity in their houses [22, 23]. In this case, home-ownership may be less secure than rental housing, particularly if the home-owner is made unemployed or becomes chronically ill. Mortgage payment commitments and the costs of maintaining housing can be stressful and the quality of housing that can be afforded on reduced incomes may be less health promoting than rental housing that can be afforded for the same expenditure [17, 24].
Housing quality is also an intervening variable between SES and health in producing social inequalities in health. Cold, damp, mouldy housing affects people's health and well-being, as well as their use of health services [25, 26]. Housing conforms to the inverse care law first identified in health care in Britain . Colder and windier parts of the UK have poorer housing, which is associated with reduced lung function, as well as raised diastolic and systolic blood pressure . People living in cold homes are more likely to have poorer mental health . Those in single-person households tend to have higher living costs and are more likely to suffer from fuel poverty, i.e. they need to spend more than 10% of their income on household energy to maintain indoor temperatures to an adequate level [30, 31]. Fuel poverty has been exacerbated by the retail price of domestic fuel increasing by 91% between 2002 and 2009 . Experiencing financial difficulties in general may well capture fuel poverty in particular.
Le Grand has argued that housing is no different from any other good in a capitalist society and should be considered fundamentally in monetary terms . The contrary view is that the ontological security provided by housing is high on the hierarchy of needs and confers a unique range of services. Analysis of the Joseph Rowntree Foundation Poverty and Social Exclusion Survey showed that poor renters were significantly more likely to be dissatisfied with their neighbourhoods (10% vs 4%), but poor home-owners were more likely to report a structural problem with their house, such as a leaky roof (13% vs 4%) . Poor home-owners were more likely to report poor mental health than renters, but this result was not significant.
Housing and mental health
Physical and mental health are clearly interconnected, but research on housing and mental health is particularly underdeveloped . There is sufficient evidence to suggest that the type and quality of housing affects psychosocial processes, which in turn can affect mental health in a variety of ways, such as identity and self-esteem, anxiety about structural hazards, worry and lack of control over maintenance and fear of neighbourhood crime [35, 36]. A cross-sectional survey of adults in two electoral wards in one northern London borough, which had independent measures of the built environment and controlled for SES and structural problems in the houses, found a significant increase in cases of depression in those living in newer housing where access was from a common balcony .
While around 16% of the English Longitudinal Survey of Ageing participants report housing problems, there have as yet been few analyses that link housing problems with any health measures .
While most of these data come from cross-sectional studies, in this paper, we use data from the longitudinal Whitehall II study, which have many advantages, but some disadvantages. People were recruited in middle years and there has been a high retention rate; the oldest cohort member was born in 1930, the youngest in 1952. While basically a London cohort, there is still considerable variation in housing quality, as in the UK as a whole .
On the other hand, the cohort is clearly skewed towards those who are employed in higher socio-economic positions and, as a consequence, there is a higher rate of home ownership than in the population as a whole, although there is still heterogeneity.
We explore the relationship between housing tenure, housing quality and household financial security over the adult life course on the mental health of older people, who are approaching retirement age or retired. Our hypothesis is that, controlling for other confounding factors:
1. Older people, who own their house, have better housing quality and fewer financial problems have fewer mental health problems than those people who rent their house.
2. The effect of these housing factors on mental health increases as people age.