Comment: Every year, at around this time, we are warned that the World Health Organisation recommends that houses should be kept at a minimum of 18C inside. Recently the lead story on RNZ Morning Report featured a health researcher emphasising that this applies to the whole house at all times, including bedrooms throughout the night.
The following day, the 7am news on the same programme featured results from a related group of Wellington researchers. Their published survey of a small and select sample of households found high carbon dioxide concentrations in bedrooms, indicating “inadequate overnight ventilation”. One of the solutions they recommended was to open windows.
Confronted by the notion that we should maintain bedrooms at a temperature of 18C or higher, with windows kept open, a colleague asked me: “Do these people live on the same planet?”
So how convincing is the scientific evidence for a minimum temperature of 18C? Before addressing this question, I would like to make two points. First, New Zealand still has far too many cold and damp houses, often plagued by mould, and there can be no doubt these are harmful to the health of adults and children. Second, I have huge admiration for the WHO, for which I was an adviser for over 30 years. Though it has improved the health of countless millions of people, including New Zealanders, its committees are not infallible. Moreover, like all of us involved in health care, they often have to give advice based on limited evidence.
The WHO supports more than 190 countries, with very different climates and ways of life. They range from countries in tropical regions (where excessive temperatures may be the main challenge) to northern parts of Europe and North America (where central heating is the norm).
Until the early 1980s, the WHO recommended an indoor temperature range from 15C to 25C. A WHO working group in 1982, which was actually focused on the needs of the elderly, concluded there was minimal risk to the health of sedentary people when the ambient temperature was between 18C and 24C.
Experts have pointed out that no references were supplied to explain the change in minimum from 15C to 18C. The suggested threshold of 18C has been echoed in subsequent WHO reports. Importantly, however, the latest WHO Housing and Health Guidelines acknowledge that “current evidence is insufficient to establish the precise temperature below which adverse health effects are likely to occur”.
Obtaining reliable evidence about safe household temperatures is actually very difficult. It might be easy to show, for example, that children living in the coldest homes suffer more chest infections leading to hospital admission, but how much of this is due to household temperatures, as opposed to overcrowding, poor nutrition, and other consequences of poverty and deprivation? Epidemiologists can try to adjust for such confounding factors, but the adjustments can never be wholly adequate.
Some researchers have resorted to laboratory experiments using healthy volunteers, but the artificial conditions (and short-term endpoints) make it difficult to extrapolate their findings to the real world of human health.
There are remarkably few studies of any quality available. Some of these were reviewed by Public Health England. This review was refreshingly honest about the lack of robust evidence. It offered a carefully worded conclusion: “Heating homes to at least 18C in winter poses minimal risk to the health of a sedentary person, wearing suitable clothing.” Referring to the “weak evidence to support this threshold”, it also recommended that “some nuancing of the message is needed to allow flexibility above and below the threshold to allow individuals to tailor their own actions”.
What about bedrooms? Though the PHE report suggested that “maintaining the 18C threshold overnight may be beneficial to protect the health of those over 65 years or with pre-existing medical conditions”, it gave different advice for the majority of the population. It stated: “Overnight, the 18C threshold may be less important for healthy people (1 – 64) if they have sufficient bedding, clothing and use thermal blankets or heating aids as appropriate.”
For children under 12 months, the United Kingdom already had a recommendation for reducing the risk of the Sudden Infant Death Syndrome – that rooms in which infants sleep should be heated to between 16C and 20C.
It’s not all about health
Choosing temperatures for rooms in our homes is not just about avoiding illness. We want to be comfortable. If I were seated in a chair, reading a book, I would like the temperature of the room to be higher than 18C. Warmth in winter can also bring pleasure. Most of us enjoy sitting by a roaring fire with friends, even if we remember that the fire produces indoor pollutants that would be frowned on by environmental health experts.
Another consideration is expense. The surging cost of living means that many New Zealand families are struggling, even to feed their children. They must feel dreadful, when told their children’s health depends on heating all bedrooms to at least 18C throughout the night.
Even people who are well off financially may not want to spend money on heating rooms to temperatures that are higher than necessary for comfort.
Apart from expenditure for individual families, there are implications for national energy sufficiency and for the carbon emissions that are powering climate change.
Individual preferences
Arbitrary temperature thresholds do not take account of whether people are active (for example, doing housework) or wearing warm clothes. As houses become warmer, their occupants tend to wear lighter clothing – and this accentuates a need for greater warmth. I have watched this process over the years in the United Kingdom, since living there for most of the 1970s. The winters were colder than anything I had experienced in New Zealand. Central heating has become far more common in Britain, and clothing habits have changed accordingly. An English colleague said to me: “When I was young, we wore at least two jerseys while doing our homework; now people expect to wander around the house in their negligee!”
There is great variation in individual preferences. Although I am well past 65, I prefer to sleep in a warm bed in a room with a temperature lower than 18C. When I stay in hotels, I often need to work out how to turn down the thermostat. The benefits of a good night’s sleep, for physical and mental health, are better established than effects of room temperature.
The New Zealand situation
Housing stock in New Zealand is improving, but there is still much work to be done. The latest media commentary was prompted by publication of a survey of indoor temperatures in different regions. This study, conducted by BRANZ, is impressive and fascinating.
My only concern is that the authors accept uncritically the “healthy recommended minimum of 18C”. But at least their study focuses on living rooms and bedrooms, during the hours when they are occupied – rather than promoting the idea that all parts of a house need to be at 18C or higher at all times.
The latter concept could be described as “making the perfect the enemy of the good”. As I have suggested, however, a threshold of 18C is not necessarily “perfect” for everyone. Parents have no need to feel worried or guilty if they are not meeting a standard that has no good scientific basis.
Our priority should be to assist families living in the coldest houses, especially if these are damp and overcrowded. I am worried that agencies may not take this challenge seriously, if they are put off by recommendations that are seen as impracticable and hard to justify. We must improve insulation, heating, and ventilation in those coldest homes in our community – for comfort and for health.
