"I think the main message is that housing improvement can improve health, especially if it's warmth and energy improvements targeting people with respiratory illnesses," said Hilary Thomson, the study's lead author from the Medical Research Council in Glasgow, UK.
They write in the journal The Cochrane Library that doubts arise because researchers have trouble teasing apart the effects of poor housing and other factors that may play a role, such as age and poverty.
The most common housing conditions tied to poor health, they write, are air quality, heat and humidity conditions, radon, noise, dust, tobacco smoke, falls and fires.
To see whether improving the physical conditions in homes could translate into tangible improvement in residents' health, the researchers pooled information from 39 previously published studies on the topic.
The past research examined a number of possible housing improvements, including refurbishing existing homes, relocating people to new homes and providing bathrooms.
Most of the data from these disparate studies could not be combined into a single pool for analysis because the research designs were too different. So instead, Thomson's team concentrated on the results that stood out across studies.
Overall, they found, programs that improve temperature control in the homes of people who are in poor health and in the worst quality housing lead to the greatest benefit, compared to improvements that are applied to whole areas of housing regardless of need.
For example, two studies from New Zealand targeted people who lived in homes with inadequate heating. They added insulation to better regulate the homes' temperature and found that the number of children and adults listed in "poor or fair health" fell by about 50 percent, relative to a comparison group with no housing changes.
"I would say it's modest improvements, but they were seen (within) about six months of the improvements. It doesn't take a while to see these improvements, they happen quite quickly," Thomson said.
A UK study found more mixed results when it looked at heating improvements throughout an entire community, without a focus on particularly needy homes.
Thomson's group cautions in their report that the results from the New Zealand studies could have been more robust because they targeted a specific population while the UK study did not.
Furthermore, they write, improving temperature control throughout homes may benefit both physical and mental health by increasing the amount of usable space. Ultimately, that may lead to better relationships between the people living in the home, and better work and school attendance.
Rebecca Morley, executive director of the National Center for Healthy Housing in Columbia, Maryland, told Reuters Health that she felt the new review was incomplete, because it did not look at studies on lead, radon and other household hazards like asbestos.
"We certainly want people to be comfortable and warm in their homes, but it's not the only concern in the U.S.," said Morley, who was not involved in the new research.
Thomson said they excluded those hazards from the review because they are already known to be toxins (so "improving" them would be expected to benefit health), but she added that it would be useful to look at them too in another study.
"Although the evidence has increased, it's still good to evaluate ongoing housing improvements and see more specifically what type of housing improvement is going to benefit who," Thomson said.
SOURCE: http://bit.ly/10Hdobt The Cochrane Library, online February 27, 2013.