Public Health England's 2014 cold weather plan notes that winter weather has a direct effect on the incidence of: heart attack, stroke, respiratory disease, flu, falls and injuries and hypothermia. Indirect effects include mental health problems such as depression, and the risk of carbon monoxide poisoning if boilers, cooking and heating appliances are poorly maintained or poorly ventilated.

The strongest link is between respiratory deaths and the cold. But because generally more people die from cardiovascular disease, cardiovascular illnesses and deaths account for a greater number of health problems. Overall, the number of excess winter deaths varies between years – generally it's around 24,000 in England and Wales. The number of excess deaths in 2013/14 was 18,200.

This represented the lowest figure since 1950/51 and reflects a prolonged period of milder than average weather after November 2013. The 5‑year moving average shows a decreasing trend in recent years up to 2005/06, after which there has been a gradual rise (Office for National Statistics statistical bulletin: excess winter mortality in England and Wales, 2013/14). It is too early to tell whether the low figures for 2013/14 represent a new downward trend.

Most excess winter deaths and illnesses are not caused by hypothermia or extremes of cold. Rather, they are usually caused by respiratory and cardiovascular problems during normal winter temperatures – when the mean outdoor temperature drops below 5°C to 8°C (Department of Health's Making the case). The risk of death and illness increases as the temperature falls further. However, because there are many more relatively 'warm' winter days than days of extreme cold, most cold‑related ill health and death occurs during these milder periods.

Unlike illnesses and deaths associated with hot days (when the increase in the number of deaths lasts for a day or so after the heatwave) rates remain higher for up to 2 weeks after a cold spell has ended.

A household that cannot afford to heat its home is likely to be under stress, for instance, from being forced to live in the only heated room. Or it may need to choose between heating and food or other commodities or risk falling into debt.

Housing conditions

Housing conditions are a very important factor. The death rate rises about 2.8% for every degree Celsius drop in the external temperature for those in the coldest 10% of homes. This compares with a 0.9% rise in deaths for every degree Celsius drop in the warmest 10% of homes (Joseph Rowntree Foundation's cold comfort). The Marmot review team's the health impacts of cold homes and fuel poverty estimated that 'excess winter deaths in the colder quarter of housing were almost 3 times as high as in the warmest quarter'.

The importance of housing conditions is also emphasised by international comparisons that show lower rates of excess winter deaths in countries where homes are more energy‑efficient.

Several factors also influence whether someone finds themselves living in a cold home – and how ill they may become as a result. These include:

  • how efficient the heating system is

  • how well insulated the home is

  • whether the person can afford to heat their home (factors here include their income, the cost of fuel, the temperature needed to make the home feel warm enough and how long the heating needs to be on)

  • the person's vulnerability to the effects of cold due to age or a medical condition.

Figure 1 shows the relation between these factors and their potential effect on health. Note that it is intended to give a simplified depiction of the complex interconnections between temperature, buildings, heating systems, cost, behaviours and health outcomes.

Figure 1 Factors linking cold temperatures to excess winter deaths and illness
Figure 1 Factors linking cold temperatures to excess winter deaths and illness

Keeping homes warm: SAP ratings

How well buildings retain heat (often expressed as a standard assessment procedure or SAP rating) is an important factor in determining how much it will cost to keep housing at a given temperature. The SAP rating of housing stock across England varies considerably. In 2012 the average was 59 (out of 100). The proportion of energy‑efficient housing (currently considered to be above 69) increased from 2% in 1996 to 18% in 2012. Around 2 million properties (9% of the housing stock) had a SAP of less than 30.

SAP scores vary according to the type of construction, level of insulation and type of heating system and its associated costs. Housing with insulated cavity walls, insulation to walls and roofs and central heating tend to have higher scores. Properties reliant on traditional forms of electric heating (such as storage heaters) may have a lower SAP score.

Older properties tend to have lower SAP scores (they are more likely to be less well insulated). The lowest rating is for pre‑1919 stock (mean score 41) and the highest is for post‑1980 housing (mean score 63).

Average SAP scores vary for different tenures. Average SAPs in the social sector (local authority and registered social landlord housing) are generally higher (around 60). They are generally lower in the owner‑occupied sector (around 50) and particularly the private rented sector (around 45).

Keeping homes warm: affordability

Living in a relatively energy‑efficient home is not the only factor influencing whether someone can keep their home warm. The affordability of the energy needed (determined by the cost of fuel and household income) is a key factor.

A 2010 study, the Centre for Sustainable Energy's understanding fuel expenditure: fuel poverty and spending on fuel, identified groups who had found it particularly difficult to pay for adequate heating. The study found that households generally consume less fuel than they need, calculated from the 2007 Department for Communities and Local Government's English house condition survey. On average, households use only around two‑thirds of the energy they actually need to stay warm enough at home. People on low incomes are more likely than average to use less heating.

Vulnerable and disadvantaged groups

In England, spending a high proportion of income on fuel tends to be associated with a low income rather than high heating needs. This pattern of expenditure tends to be associated more closely with some groups, such as lone parents.

The 2010 Centre for Sustainable Energy you just have to get by survey looked at people living on less than 60% of the national median income. Half said they found it difficult to pay their fuel bills. During the previous winter, nearly half (46%) had cut back on heating and 63% had lived in homes that were colder than they wanted them to be. Nearly half (47%) said the cold had made them feel anxious or depressed, and 30% said an existing health problem had got worse. Some (17%) did not feel able to invite friends or family to the home because of the cold.

Some groups are particularly vulnerable to cold homes. Again, this is caused by a variety of factors. For example, some people are likely to spend a larger part of their time at home, increasing both the likely cost of heating and their potential exposure to an inadequately heated home.

Excess winter deaths are more common among, but are by no means confined to, older people. In 2013/14 ('Statistical bulletin: excess winter mortality in England and Wales, 2013/14'):

  • 51% of cold‑related deaths were among people aged 85 and older

  • 27% were among those aged between 75 and 84

  • 22% were among people under 75.

Others, such as people with respiratory conditions, or an increased susceptibility to respiratory infections, are also likely to be at increased risk of health problems caused by living in a cold home.

Fuel poverty

Fuel poverty relates to a household's ability to pay for adequate heating. It can be caused by some or all of the following:

  • a poorly insulated home

  • inefficient or inadequate heating

  • high fuel prices

  • low income

  • type of residents – for example, pensioners and disabled people may spend more time at home and therefore need heating on more often.

In England, the definition of fuel poverty changed after the 2012 Department of Energy and Climate Change Hills review. It is now measured using the 'low income high cost' indicator. This means a household is said to be 'fuel poor' if its members are living below the official poverty line and have higher than average energy costs.

A previous definition (still in use in Wales, Scotland and Northern Ireland) is that someone is in fuel poverty if they need to spend more than 10% of their income on domestic energy bills to keep their home warm enough.

National policy

National policy linked to cold homes is driven by health (Public Health England's 2014 cold weather plan), fuel poverty (Department of Energy and Climate Change's cutting the cost of keeping warm) and environmental issues (Department of Energy and Climate Change's reducing the UK's greenhouse gas emissions by 80% by 2050 and 2013 Home Energy Conservation Act reports).

For instance, people on a low income may need to use more fuel to keep warm in poorly insulated housing. So any increase in fuel prices, either as a result of funding for insulation schemes or to reduce fuel use, will push some people into (or deeper into) fuel poverty. This will be true unless the increase in fuel prices coincides with, for example, improvements to the insulation of their own homes.

The suitability of accommodation is one of the factors that must be considered by local authorities under their general duty to promote wellbeing when carrying out their care and support functions under the Care Act 2014.