(Inside Science) -- In 2003, the hottest summer in more than 400 years hit Europe, killing 70,000 people. Most of the victims were elderly. People are more affected by temperature as they age -- the summers feel hotter and the winters feel colder. But why are heatwaves so dangerous to older people? And what can we do to minimize deaths from the next record-breaking summer? As global warming makes temperature extremes more likely, it's as important as ever to understand how humans beat the heat.
When humans are hot, either from exercising or when it’s hot outside, they sweat -- releasing heat through evaporative cooling. But they get even more cooling power by pumping lots of blood to the skin, where it loses heat out to the environment.
According to Larry Kenney, exercise physiologist at Pennsylvania State University, "One of the unique things about humans is their ability to increase blood flow to the skin. When we’re hot we pump a lot of blood to the skin and the vessels dilate, -- that’s why the skin looks red when it’s hot outside."
For many years, researchers at Penn State have studied how aging affects how we regulate our temperature. At first they focused on sweating.
“Originally we thought, as a lot of people thought, that older people were less able to tolerate heat because something happened to the sweat glands in their skin. They just produced less sweat as the skin aged, sweat glands atrophied or went away. It turns out that’s not the case. In fact, sweating is a lot more related to how fit you are, how acclimated to the heat you are and how well hydrated you are than it is to age. But what does change with aging is blood flow to the skin," said Kenney.
Kenney's lab uses a special technique, called laser speckle contrast imaging, to take pictures of blood flow within the skin. Researchers shine a laser on the skin of volunteers and record the dots, or speckles, that bounce back.
Blood flow causes the speckles to move around. A computer tracks the movement and assigns a color depending on the level of activity. Spots with a lot of blood flow show up red and yellow, while areas with less movement show up blue. Unlike other imaging techniques, it can look at large areas of skin, like a whole hand or foot.
In hot weather, a person may pump up to 20 times more blood to the skin than in cold weather. But older people run into trouble.
“As older people try to pump blood flow to the skin they have two problems. One, the vessels in the skin don’t dilate as well, and number two, even though the vessels don’t dilate as well, the heart continues to try to forcefully pump blood out. So, heat stress results in cardiovascular strain, increased strain on the heart,” said Kenney.
The majority of people killed by heatwaves don’t die of heat stroke or dehydration. They die from heart problems such as heart attacks or heart failure.
"One of the important molecules in the skin and in other blood vessels that allows them to fully dilate is nitric oxide. Nitric oxide is produced in the endothelium of the blood vessels -- the single cell layer lining the blood vessels. Older subjects have less nitric oxide available and that’s one of the reasons they don’t dilate their skin arterials as much when their body heats up," said Kenney.
Kenney and his colleagues are investigating whether one way to boost nitric oxide in the blood vessels of older people, would be to take supplements of vitamin B9, also known as folic acid.
The idea is that the body can take folic acid and turn it into another molecule called BH4. BH4 in turn helps make nitric oxide. In a recent study, Kenney and his colleagues tested how well folic acid supplements could improve blood flow in older adults.
"Every day they took folic acid supplements and when we did that we were able to show both acutely, like the same day they took the vitamin, and then over a six-week period, that their skin blood flow was improved. So, that’s one we found a very low cost way to improve skin blood flow in the elderly," said Kenney.
People over 80 are the fastest growing demographic in the world. Finding ways to help improve the health of this older population, especially during heat waves, could help save lives.