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How rising temperatures affect our health
19 September 2019
This story is part of Covering Climate Now, a global collaboration of more than 250 news outlets to strengthen coverage of the climate story.
Global warming is accelerating, driven by the continuing rise in greenhouse gas emissions. Australia’s climate has warmed by just over 1°C since 1910, with global temperatures on course for a 3-5°C rise this century.
Australia is ahead of the global temperature curve. Our average daily temperature is 21.8°C – that’s 13.7°C warmer than the global average of 8.1°C.
So what do high temperatures do to our bodies? And how much extra heat can people and our way of living tolerate?
More scorchers ahead
Australia’s summer of 2018-19 was 2.14°C warmer than the 1961–90 average, breaking the previous record set in 2012–13 by a large margin. It included an unprecedented sequence of five consecutive days with nationally averaged maximum temperatures above 40°C.
The Bureau of Meteorology (BOM) has warned this summer will be another scorcher. Hot dry northerly winds tracking across drought-affected New South Wales and Queensland have the capacity to deliver blistering heat and extreme fire risks to the southern states, and little relief is in sight for those in drought.
Some rural Australians have already been exposed to 50°C days, and the major southern metro cities are set to do the same within the next decade or so.
How our bodies regulate heat
Quietly sitting indoors with the air temperature about 22°C, we passively generate that additional 15°C to keep our core temperature at about 37°C.
Even when the air temperature is 37°C, our metabolism continues to generate additional heat. This excess internal heat is shed into the environment through the evaporation of sweat from our skin.
Temperature and humidity gradients between the skin surface and boundary layer of air determine the rate of heat exchange.
When the surrounding air is hot and humid, heat loss is slow, we store heat, and our temperatures rises.
That’s why hot, dry air is better tolerated than tropical, humid heat: dry air readily absorbs sweat.
A breeze appears refreshing by dislodging the boundary layer of saturated air in contact with the skin and allowing in drier air – thus speeding up evaporation and heat shedding.
What happens when we overheat?
Heat exposure becomes potentially lethal when the human body cannot lose sufficient heat to maintain a safe core temperature.
When our core temperature reaches 38.5°C, most would feel fatigued. And the cascade of symptoms escalate as the core temperature continues to rise beyond the safe functioning range for our critical organs: the heart, brain and kidneys.
While some heat-acclimatised elite athletes, such as Tour de France cyclists, may tolerate 40°C for limited periods, this temperature is potentially lethal for most people.
As a pump, the heart’s role is to maintain an effective blood pressure. It fills the hot and dilated blood vessels throughout the body to get blood to vital organs.
Exposure to extreme heat places significant additional workload on the heart. It must increase the force of each contraction and the rate of contractions per minute (your heart rate).
If muscles are also working, they also need an increased blood flow.
If all this occurs at a time when profuse sweating has led to dehydration, and therefore lower blood volume, the heart must massively increase its work.
The heart is also a muscle, so it too needs extra blood supply when working hard. But when pumping hard and fast and its own demand for blood flow is not matched by its supply, it can fail. Many heat deaths are recorded as heart attacks.
High aerobic fitness levels offer some heat protection, yet athletes and fit young adults pushing themselves too hard also die in the heat.
Who is more at risk?
Older Australians are more vulnerable to heat stress. Age is commonly associated with poorer aerobic fitness and impaired ability to detect thirst and overheating.
Obesity also increases this vulnerability. Fat acts as an insulating layer, as well as giving the heart a more extensive network of blood vessels to fill. The additional weight requires increased heat-generating muscular effort to move.
Certain medications can lower heat tolerance by interfering with our natural mechanisms necessary to cope with the heat. These include drugs that limit increases in heart rate, lower blood pressure by relaxing blood vessels, or interfere with sweating.
Core temperatures are increased by about half a degree during late stage pregnancy due to hormonal responses and increased metabolic rate. The growing foetus and placenta also demand additional blood flow. Exposure of the fetus to heat extremes can precipitate preterm birth and life-long health problems such as congential heart defects.
Won’t we just acclimatise?
Our bodies can acclimatise to hot temperatures, but this process has its limits. Some temperatures are simply too hot for the heart to cope with and for sweat rates to provide effective cooling, especially if we need to move or exercise.
We’re also limited by our kidneys’ capacity to conserve water and electrolytes, and the upper limit to the amount of water the human gut can absorb.
Profuse sweating leads to fluid and electrolyte deficits and the resulting electrolyte imbalance can interfere with the heart rhythm.
Mass death events are now occurring during heat waves in traditionally hot countries such as India and Pakistan. This is when heat extremes approaching 50°C exceed the human body’s capacity to maintain its safe core temperature range.
Heatwaves are hotter, more frequent and lasting longer. We can’t live life entirely indoors with air conditioning as we need to venture outdoors to commute, work, shop, and care for the vulnerable. People, animals and our social systems depend on this.
Besides, on a 50°C day, air conditioning units will struggle to remove 25°C from the ambient air.
How often should I get my teeth cleaned?
27 August 2019
If you went to your dentist for a check-up and dental clean in the last year, give yourself a pat on the back. Not everyone loves the dentist, but research shows people who visit at least once a year for preventative care are happier with their smile.
Regular dental visitors are also less likely to need a filling or have a tooth removed.
So how often do we need to go to the dentist? Most of us can get away with an annual trip, but some people at higher risk of dental problems should visit more often.
Why do I need to get my teeth cleaned?
While we all do the best we can on our own, professional teeth cleaning removes plaque, the soft yellowish build-up, and calculus (hardened plaque) we can’t get to. This soft build-up is made up of billions of different types of bacteria that live and reproduce in our mouth by feeding on the food we eat.
Most bacteria live in our bodies without causing too much trouble. But certain bacteria in dental plaque, when they grow in numbers, can lead to cavities (holes in the teeth) or gum disease.
A dental clean will reduce your chance of getting cavities or gum disease by significantly reducing the amount of plaque and calculus in your mouth.
So how often?
As a dentist, my patients often ask me how regularly they should get their teeth cleaned. My response is usually: “That depends”.
Most private health insurance schemes cover a dental check-up and clean once every six months. But there’s no hard and fast evidence, particularly if you’re a healthy person who is less likely to get a cavity or gum disease.
However, some people are at higher risk of getting dental cavities or gum disease – and this group should get their teeth cleaned more often.
Hole in one
We know certain health and lifestyle factors can affect a person’s risk of developing cavities. Here are some yes/no questions you can ask yourself to understand whether you’re at a higher risk:
- is your drinking water or toothpaste fluoride-free?
- do you snack a lot, including on sweets?
- do you avoid flossing?
- do you brush your teeth less than twice a day?
- do you visit your dentist for toothaches rather than check-ups?
- do you need new fillings every time you visit the dentist?
- is your dentist “watching” a lot of early cavities?
- do you have to wear an appliance in your mouth such as a denture or braces?
- do you suffer from a chronic long-term health condition such as diabetes?
- do you suffer from a dry mouth?
If you answered “yes” to most of these questions, you’re likely to need to see your dentist or hygienist at least every six months, if not more often.
As well as removing the bug-loaded plaque and calculus, people prone to cavities benefit from the fluoride treatment after scaling.
Evidence shows professional fluoride treatment every six months can lead to a 30% reduced risk of developing cavities, needing fillings or having teeth removed.
Dental health is related to our overall health
People taking blood thinners and other medications, such as pills and infusions for osteoporosis, may need to visit the dentist more regularly too. These medications can complicate the process of an extraction or other dental work, so regular checks and cleans are best to help detect problems before they become serious.
People with bleeding gums should also see their dental practitioners more often. This is especially important if you have been diagnosed with advanced gum disease, known as periodontal disease.
What about the budget?
The average cost of a check-up, dental clean and fluoride treatment is A$231, but the cost can vary from A$150 to A$305. You can contact your local dentist to find out what they charge. Your dentist may offer you a payment plan.
If you can’t afford this, you may qualify for free or discounted treatment if you hold a concession card. Children from families that receive a Family Tax Benefit A may be eligible for free dental treatment through the Child Dental Benefits Schedule.
People with private health insurance with extras or ancillary cover will also have some or all of their dental treatment covered.
Protecting your smile
So you don’t really get cavities or have gum disease, but would prefer to see your dentist every six months? Great. Some people prefer to go twice a year to reduce the chance of a nasty toothache.
Parents often wish to set a good example for their children by making regular check and clean appointments for the whole family.
There are many benefits to regular checks and cleans. Visiting your dentist regularly helps reduce the chance of needing more complex and expensive dental treatment later on.
And touching base with your oral health practitioner provides that nudge we all need now and again to eat healthily, brush better and floss more often.
Rat detective uses DNA to uncover how rats scurry around cities
13 August 2019
It’s dark and I’m parked in an alley near a lopsided compost bin. I have a notepad, binoculars and a lukewarm cup of coffee — everything needed for a successful stakeout. I am waiting for them.
They appear approximately one hour before dawn, skittering from dumpster to dumpster along old paths they have worn down with time. I am trying to track their movements, to understand how far they go and how often. But it’s clear to me that the traditional detective approach isn’t going to work. There are too many and they move in places where I can’t follow. I’ll have to track them a different way — I’m going to need some rat DNA.
Take a trip to a city almost anywhere in the world and odds are that you will find rats. Rats are infamous for travelling with us across the globe and yet, until recently, there was very little information on how rats move within cities.
Slippery little fellas
As someone who has trapped more than 700 rats, I can tell you that this lack of information is partly because rats are notoriously difficult to study. For other wildlife species, you can track movement by trapping an animal, tagging it with something like a numbered ear tag, recapturing that animal later on and then measuring the distance between traps. But rats are wary of traps, and very few rats will re-enter them more than once.
To get around issues of trappability, researchers can use GPS technologies. This approach still involves wrangling rats to affix GPS tags, but advances in GPS technologies allow for data to be transmitted to the researcher remotely without having to catch the animal again. In fact, miniaturization of tags has allowed us to attach GPS tags to rats. But we’ve learned that GPS tags are tricky to use with urban rats because they will remove them and satellite signals are obstructed in cities. Thank you, next?
An alternative to these approaches involves collecting rat DNA. Chances are you’ve heard of companies like 23andMe that track your global ancestry by sequencing DNA from your saliva. This approach looks at similarities and differences in the genetic codes of individuals to make inferences about how similar your DNA sequence is to that of other people in the database. This can also be applied to rats. Indeed, researchers have used genetics to track the migration of rats globally. But how can this information help us to understand and address rat-associated issues?
Staying close to home
When sampled across a city, we can trace rat movement at a finer scale. Over the past 10 years, there has been an increase in the number of rat movement studies using genetics. By looking at relatedness of individuals based on genetic similarity, we can identify groups of relatives. We’ve found that relatives are often in close proximity to each other.
In Vancouver, most relatives are within approximately 50 metres of each other and relatedness tends to decrease past 250 metres; on the whole, rats probably don’t move very far.
However, some rats travel further afield. In Baltimore, one rat was estimated to have moved up to 11.5 kilometres. These migrant individuals can be identified because their genetic information assigns them to a group of individuals in a different location than to the one in which they were caught.
Thanks to genetics, we have come to understand that while rats typically move about the space of a city block, they move further than was estimated by observational methods. This is useful to know because it can help inform how we address rat-associated concerns.
Pathogens on the block
Rats carry a number of disease-causing organisms that can be transmitted to people. Many of these are spread among rats and to people through close contact with affected rats and their urine or feces. In Vancouver, where rats rarely move between blocks, we would expect that the pathogens they carry would be restricted as well, due to few opportunities to spread.
And that’s what we see. Some blocks have many rats carrying a particular pathogen, while a neighbouring block may have few or no affected rats. This is important because it suggests that actions that disrupt the normal patterns of rat movement could affect pathogen spread.
To remove rat-associated disease risks, efforts have focused on eliminating rats altogether, but this approach has been largely ineffective. This is partly because we fail to appropriately scale our control response.
Most control efforts are enacted at a single property. If we look to the DNA, however, we see why that approach won’t cut it. Rats and rat colonies are often not restricted to a single property. For control efforts to be effective, they must encompass the genetic group, termed an eradication unit.
The scale of the unit varies by location due in part to barriers to movement such as roadways or rivers. For example, in Vancouver a genetic cluster of related rats occupies an entire block, or spans several blocks. By comparison, researchers have found that an eradication unit might encompass an entire “valley” in Salvador, Brazil.
From my vantage point in the alley, I am struck by the power of genetic sequencing to help us answer challenging questions. Instead of viewing each rat independently, I begin to see them as interconnected groups of relatives scurrying along the pavement. I wonder if any are outsiders, migrants from another block.
I check my bag and realize that something’s missing. Tomorrow I’ll be back with what I need for DNA collection: my Rat Detective Toolkit 2.0.