Does the time of day you move your body make a difference to your health?

Undertaking the majority of daily physical activity in the evening is linked to the greatest health benefits for people living with obesity, according to researchers from the University of Sydney, Australia who followed the trajectory of 30,000 people over almost 8 years.

Using wearable device data to categorise participant's physical activity by morning, afternoon or evening, the researchers uncovered that those who did the majority of their aerobic moderate to vigorous physical activity- the kind that raises our heartrate and gets us out of breath- between 6pm and midnight had the lowest risk of premature death and death from cardiovascular disease.

The frequency with which people undertook moderate to vigorous physical activity (MVPA) in the evening, measured in short bouts up to or exceeding three minutes, also appeared to be more important than their total amount of physical activity daily.

The study, led by researchers from the University's Charles Perkins Centre is published in the journal Diabetes Care today.

"Due to a number of complex societal factors, around two in three Australians have excess weight or obesity which puts them at a much greater risk of major cardiovascular conditions such as heart attacks and stroke, and premature death," said Dr Angelo Sabag, Lecturer in Exercise Physiology at the University of Sydney.

"Exercise is by no means the only solution to the obesity crisis, but this research does suggest that people who can plan their activity into certain times of the day may best offset some of these health risks."

Smaller clinical trials have shown similar results, however the large scale of participant data in this study, the use of objective measures of physical activity and hard outcomes, such as premature death, makes these findings significant.

Joint first author Dr Matthew Ahmadi also stressed that the study did not just track structured exercise. Rather researchers focused on tracking continuous aerobic MVPA in bouts of 3 minutes or more as previous research shows a strong association between this type of activity, glucose control and lowered cardiovascular disease risk compared with shorter (non-aerobic) bouts.

"We didn't discriminate on the kind of activity we tracked, it could be anything from power walking to climbing the stairs, but could also include structured exercise such as running, occupational labour or even vigorously cleaning the house," said Dr Ahmadi, National Heart Foundation postdoctoral research fellow at the Charles Perkins Centre, University of Sydney.

While observational, the findings of the study support the authors original hypothesis, which is the idea -- based on previous research -- that people living with diabetes or obesity, who are already glucose intolerant in the late evening, may be able to offset some of that intolerance and associated complications, by doing physical activity in the evening.

The researchers used data from UK Biobank and included 29,836 adults aged over 40 years of age living with obesity, of whom 2,995 participants were also diagnosed with Type 2 diabetes.

Participants were categorised into morning, afternoon of evening MVPA based on when they undertook the majority of their aerobic MVPA as measured by a wrist accelerometer worn continuously for 24 hours a day over 7 days at study onset.

The team then linked health data (from the National Health Services and National Records of Scotland) to follow participants health trajectory for 7.9 years. Over this period they recorded 1,425 deaths, 3,980 cardiovascular events and 2,162 microvascular disfunction events.

To limit bias, the researchers accounted for differences such as age, sex, smoking, alcohol intake, fruit and vegetable consumption, sedentary time, total MVPA, education, medication use and sleep duration. They also excluded participants with pre-existing cardiovascular disease and cancer.

The researchers say the length of the study follow-up and additional sensitivity analysis bolster the strength of their findings however, due to the observational design, they cannot completely rule out potential reverse causation. This is the possibility that some participants had lower aerobic MVPA levels due to underlying or undiagnosed disease.

Professor Emmanuel Stamatakis, Director of the Mackenzie Wearables Research Hub at the Charles Perkins Centre and senior author on the paper, said the sophistication of studies in the wearables field is providing huge insights into the patterns of activity that are most beneficial for health.

"It is a really exciting time for researchers in this field and practitioners alike, as wearable device-captured data allow us to examine physical activity patterns at a very high resolution and accurately translate findings into advice that could play an important role in health care," said Professor Stamatakis.

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Shutting down nuclear power could increase air pollution

Nearly 20 percent of today's electricity in the United States comes from nuclear power. The U.S. has the largest nuclear fleet in the world, with 92 reactors scattered around the country. Many of these power plants have run for more than half a century and are approaching the end of their expected lifetimes.

Policymakers are debating whether to retire the aging reactors or reinforce their structures to continue producing nuclear energy, which many consider a low-carbon alternative to climate-warming coal, oil, and natural gas.

Now, MIT researchers say there's another factor to consider in weighing the future of nuclear power: air quality. In addition to being a low carbon-emitting source, nuclear power is relatively clean in terms of the air pollution it generates. Without nuclear power, how would the pattern of air pollution shift, and who would feel its effects?

The MIT team took on these questions in a new study appearing in Nature Energy. They lay out a scenario in which every nuclear power plant in the country has shut down, and consider how other sources such as coal, natural gas, and renewable energy would fill the resulting energy needs throughout an entire year.

Their analysis reveals that indeed, air pollution would increase, as coal, gas, and oil sources ramp up to compensate for nuclear power's absence. This in itself may not be surprising, but the team has put numbers to the prediction, estimating that the increase in air pollution would have serious health effects, resulting in an additional 5,200 pollution-related deaths over a single year.

If, however, more renewable energy sources become available to supply the energy grid, as they are expected to by the year 2030, air pollution would be curtailed, though not entirely. The team found that even under this heartier renewable scenario, there is still a slight increase in air pollution in some parts of the country, resulting in a total of 260 pollution-related deaths over one year.

When they looked at the populations directly affected by the increased pollution, they found that Black or African American communities -- a disproportionate number of whom live near fossil-fuel plants -- experienced the greatest exposure.

"This adds one more layer to the environmental health and social impacts equation when you're thinking about nuclear shutdowns, where the conversation often focuses on local risks due to accidents and mining or long-term climate impacts," says lead author Lyssa Freese, a graduate student in MIT's Department of Earth, Atmospheric and Planetary Sciences (EAPS).

"In the debate over keeping nuclear power plants open, air quality has not been a focus of that discussion," adds study author Noelle Selin, a professor in MIT's Institute for Data, Systems, and Society (IDSS) and EAPS. "What we found was that air pollution from fossil fuel plants is so damaging, that anything that increases it, such as a nuclear shutdown, is going to have substantial impacts, and for some people more than others."

The study's MIT-affiliated co-authors also include Principal Research Scientist Sebastian Eastham and Guillaume Chossière SM '17, PhD '20, along with Alan Jenn of the University of California at Davis.

Future phase-outs

When nuclear power plants have closed in the past, fossil fuel use increased in response. In 1985, the closure of reactors in Tennessee Valley prompted a spike in coal use, while the 2012 shutdown of a plant in California led to an increase in natural gas. In Germany, where nuclear power has almost completely been phased out, coal-fired power increased initially to fill the gap.

Noting these trends, the MIT team wondered how the U.S. energy grid would respond if nuclear power were completely phased out.

"We wanted to think about what future changes were expected in the energy grid," Freese says. "We knew that coal use was declining, and there was a lot of work already looking at the impact of what that would have on air quality. But no one had looked at air quality and nuclear power, which we also noticed was on the decline."

In the new study, the team used an energy grid dispatch model developed by Jenn to assess how the U.S. energy system would respond to a shutdown of nuclear power. The model simulates the production of every power plant in the country and runs continuously to estimate, hour by hour, the energy demands in 64 regions across the country.

Much like the way the actual energy market operates, the model chooses to turn a plant's production up or down based on cost: Plants producing the cheapest energy at any given time are given priority to supply the grid over more costly energy sources.

The team fed the model available data on each plant's changing emissions and energy costs throughout an entire year. They then ran the model under different scenarios, including: an energy grid with no nuclear power, a baseline grid similar to today's that includes nuclear power, and a grid with no nuclear power that also incorporates the additional renewable sources that are expected to be added by 2030.

They combined each simulation with an atmospheric chemistry model to simulate how each plant's various emissions travel around the country and to overlay these tracks onto maps of population density. For populations in the path of pollution, they calculated the risk of premature death based on their degree of exposure.

System response

Their analysis showed a clear pattern: Without nuclear power, air pollution worsened in general, mainly affecting regions in the East Coast, where nuclear power plants are mostly concentrated. Without those plants, the team observed an uptick in production from coal and gas plants, resulting in 5,200 pollution-related deaths across the country, compared to the baseline scenario.

They also calculated that more people are also likely to die prematurely due to climate impacts from the increase in carbon dioxide emissions, as the grid compensates for nuclear power's absence. The climate-related effects from this additional influx of carbon dioxide could lead to 160,000 additional deaths over the next century.

"We need to be thoughtful about how we're retiring nuclear power plants if we are trying to think about them as part of an energy system," Freese says. "Shutting down something that doesn't have direct emissions itself can still lead to increases in emissions, because the grid system will respond."

Read more at Science Daily

20,000 premature US deaths caused by human-ignited fires each year

Over 80% of premature deaths caused by small smoke particles in the United States result directly from human-ignited fires. This is the outcome of a study published today in IOP Publishing's journal Environmental Research Letters.

The new study, led by researchers at the Massachusetts Institute of Technology, analyses the impact of smoke particles on air quality in the United States. Their research shows that human-ignited fires account for more than 67% of small smoke particles called PM2.5 in the United States. These particles are known to degrade air quality, causing respiratory illnesses and premature death.

The level of fire activity in the US is on the rise. The research team estimate that smoke from human-ignited fires was responsible for 20,000 premature deaths in 2018 alone, a year with a high frequency of fire events -- a substantial portion of which were associated with human ignitions such as agricultural and human lit fires. This is 270% more than there were in 2003, when there was a low frequency of fire events. The research highlights that during high fire activity years, there are much higher concentrations of smoke PM2.5 in the air.

Dr Therese Carter, lead author of the study, said: "Fires not only threaten human lives, infrastructure, and ecosystems, but they are also a major cause for concern in terms of air quality. High levels of smoke exposure can negatively impact human health resulting in conditions such as respiratory infections, lung cancer, heart disease and even premature births. Our results show that a large and significant portion of harmful smoke particles result directly from human-lit fires."

The team used the Global Fire Emissions Database to quantify agricultural fire emissions, then classify these fires into two categories: human vs. natural ignition. Applying a chemical transport model, they simulate the concentration of smoke particles across the United States, concluding that a significant portion of PM2.5 in the US results from human-ignited fires and thus has the potential to be managed.

To limit the devastating effects of pollution from small smoke particles, the team recommends an ignition-focused approach. State agencies can implement management plans to restrict the ignition of agricultural fires to periods when weather conditions would minimise health impacts. However, human-ignited wildfires are much harder to manage due to their sporadic and unplanned nature.

Read more at Science Daily

Adding salt to your food at the table is linked to higher risk of premature death

People who add extra salt to their food at the table are at higher risk of dying prematurely from any cause, according to a study of more than 500,000 people, published in the European Heart Journal today (Monday).

Compared to those who never or rarely added salt, those who always added salt to their food had a 28% increased risk of dying prematurely. In the general population about three in every hundred people aged between 40 and 69 die prematurely. The increased risk from always adding salt to food seen in the current study suggests that one more person in every hundred may die prematurely in this age group.

In addition, the study found a lower life expectancy among people who always added salt compared to those who never, or rarely added salt. At the age of 50, 1.5 years and 2.28 years were knocked off the life expectancy of women and men, respectively, who always added salt to their food compared to those who never, or rarely, did.

The researchers, led by Professor Lu Qi, of Tulane University School of Public Health and Tropical Medicine, New Orleans, USA, say their findings have several public health implications.

"To my knowledge, our study is the first to assess the relation between adding salt to foods and premature death," he said. "It provides novel evidence to support recommendations to modify eating behaviours for improving health. Even a modest reduction in sodium intake, by adding less or no salt to food at the table, is likely to result in substantial health benefits, especially when it is achieved in the general population."

Assessing overall sodium intake is notoriously difficult as many foods, particularly pre-prepared and processed foods, have high levels of salt added before they even reach the table. Studies assessing salt intake by means of urine tests often only take one urine test and so do not necessarily reflect usual behaviour. In addition, foods that are high in salt are often accompanied by foods rich in potassium, such as fruit and vegetables, which is good for us. Potassium is known to protect against the risk of heart diseases and metabolic diseases such as diabetes, whereas sodium increases the risk of conditions such as cancer, high blood pressure and stroke.

For these reasons, the researchers chose to look at whether or not people added salt to their foods at the table, independent of any salt added during cooking.

"Adding salt to foods at the table is a common eating behaviour that is directly related to an individual's long-term preference for salty-tasting foods and habitual salt intake," said Prof. Qi. "In the Western diet, adding salt at the table accounts for 6-20% of total salt intake and provides a unique way to evaluate the association between habitual sodium intake and the risk of death."

The researchers analysed data from 501,379 people taking part in the UK Biobank study. When joining the study between 2006 and 2010, the participants were asked, via a touch-screen questionnaire, whether they added salt to their foods (i) never/rarely, (ii) sometimes, (iii) usually, (iv) always, or (v) prefer not to answer. Those who preferred not to answer were not included in the analysis. The researchers adjusted their analyses to take account of factors that could affect outcomes, such as age, sex, race, deprivation, body mass index (BMI), smoking, alcohol intake, physical activity, diet and medical conditions such as diabetes, cancer and heart and blood vessel diseases. They followed the participants for a median (average) of nine years. Premature death was defined as death before the age of 75 years.

As well as finding that always adding salt to foods was linked to a higher risk of premature death from all causes and a reduction in life expectancy, the researchers found that these risks tended to be reduced slightly in people who consumed the highest amounts of fruit and vegetables, although these results were not statistically significant.

"We were not surprised by this finding as fruits and vegetables are major sources of potassium, which has protective effects and is associated with a lower risk of premature death," said Prof. Qi.

He added: "Because our study is the first to report a relation between adding salt to foods and mortality, further studies are needed to validate the findings before making recommendations."

In an editorial to accompany the paper, Professor Annika Rosengren, a senior researcher and professor of medicine at the Sahlgrenska Academy, University of Gothenburg, Sweden, who was not involved with the research, writes that the net effect of a drastic reduction in salt intake for individuals remains controversial.

"Given the various indications that a very low intake of sodium may not be beneficial, or even harmful, it is important to distinguish between recommendations on an individual basis and actions on a population level," she writes.

She concludes: "Classic epidemiology argues that a greater net benefit is achieved by the population-wide approach (achieving a small effect in many people) than from targeting high-risk individuals (a large effect but only achieved in a small number of people). The obvious and evidence-based strategy with respect to preventing cardiovascular disease in individuals is early detection and treatment of hypertension, including lifestyle modifications, while salt-reduction strategies at the societal level will lower population mean blood pressure levels, resulting in fewer people developing hypertension, needing treatment, and becoming sick. Not adding extra salt to food is unlikely to be harmful and could contribute to strategies to lower population blood pressure levels."

A strength of Prof. Qi's study is the large number of people included. It also has some limitations, which include: the possibility that adding salt to food is an indication of an unhealthy lifestyle and lower socio-economic status, although analyses attempted to adjust for this; there was no information on the quantity of salt added; adding salt may be related to total energy intake and intertwined with intake of other foods; participation in UK Biobank is voluntary and therefore the results are not representative of the general population, so further studies are needed to confirm the findings in other populations.

Read more at Science Daily