New research has linked tropical heat with higher rates of anxiety, stress and hostility, as well as fewer hours of sleep, reduced appetite and lower energy levels.

The study has been released as northern Australia enter the monsoonal build-up - the period of extreme weather tension known locally as "mango madness".

The research, which was conducted by Sue Coleman and Dr Mary Morris through Charles Darwin University, could have implications for occupational health and safety laws.

It found workers labouring under the Darwin sun typically had poorer mental health than their colleagues in air-conditioning.

Protective clothing often made the heat stress worse.

Sleep length, mood, appetite and energy levels decreased in the build-up relative to the dry season, according to the study.

In effect, the exposed workers were suffering seasonal affective disorder, a condition typically associated with northern winters and sunless days.

No more 'she'll be right'

Dr Morris, a senior lecture in psychology, said tradesmen as well as Indigenous people without access to air-conditioning were the worst affected.

"My biggest concern is for people like roofers," she said. "I know they start early and knock off early but the head load on that roof with protective clothing is phenomenal.

"We have this gorgeous laissez faire attitude in the tropics.

"We accept the fact people are more aggressive and there are more fights and more alcohol use.

"But there are a lot of people this attitude is harming - whether it's the Indigenous people who don't have as much access to air-con or cooler environments, or kids or homeless people or the average Joe Blow coming off the roof and feeling aggressive.

"The results are what they are. Air-con is better for us than non air-con and we feel better. The build-up is a negative influence on our mood and well-being."

Homicide, sexual assault increases with the build-up

Violent crime including homicide increased markedly in the Top End during the build up and wet season, despite a fall in population.

Assault including sexual assault have shown annual increases in November and December in Darwin, but property theft such as break-ins to houses have not shown a similar seasonal change.

Total offences against the person were higher in Darwin in the October to December quarter than July to September.

From 2003 to 2007 there were 44 homicides in the northernmost region of the NT. Fifty per cent (22) of these homicides occurred in the build-up months of October to December quarter. A further 13 occurred in the months of January to March quarter. There were five and four homicides in the April to June and July to August quarters respectively.

In a 12-year study released in 2008, surgeons at Royal Darwin Hospital found fracture hospitalisations were 40 per cent higher in October and November than in other months.

Per capita alcohol consumption and alcohol-attributed deaths in the NT were markedly higher than in Australia generally.

Alcohol-attributable hospitalisation was more than twice the national rate.

'Heat exhaustion deaths could be prevented'

Dr Morris said the researchers asked workers at building sites to complete a detailed questionnaire. The same workers then completed a second questionnaire six months later.

"We got the same people for both studies," she said. "We know it's these people whose moods are changing. It's the same people measured twice.

"If you live up here you're concerned your friend's children are in construction and doing various jobs like that."

"No-one has done the research into the long-term effect of heat. If you're dehydrating your body every day and putting your body under massive heat stress and heat fatigue every day, then even if you hydrate and fix it at night, is that long-term damaging?

"Is it fatiguing more than just some muscles? Are our hormones and our glands and our insulin - is that all being damaged by it?

"You can't keep messing around with your body like that and not have consequences. I don't think our bodies were designed to do that."

She said many deaths considered accidents could have been preventable. In 2005, in November during the build-up, a 25-year-old Australian Army soldier died from acute heat stroke during a training exercise in sweltering conditions at the NT's Mount Bundy facility.

The Army admitted the death was preventable.

'Hotter cities have higher crime rates'

Studies conducted in other cities have linked temperature with violent crime.

The number of individual assaults reported for each day in Chicago in June, July and August of 1977 increased with the daily temperature.

The authors of that study also found hotter US cities had significantly higher violent crimes rates. The number of serious and deadly assaults increased by 3.86 per cent per 100,000 people for every temperature increase of one degree Farenheit (0.55 degrees Celsius).