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• Some people are more sensitive to their experiences than others
• A British study set out to determine if this sensitivity is caused by the environment or genes
• They found that the environment was slightly more influential than genes in causing sensitivity

Very sensitive people may owe about half of their heightened feelings to their genes, a British study of twins suggests.

Researchers looked at pairs of identical and fraternal 17-year-old twins to gauge how much differences in sensitivity owed to genes or the environment.

While identical twins share the same genes, fraternal twins don’t, so findings among identical twins are more likely to be genetic than environmental, the researchers explained.

The study found that 47% of the differences in sensitivity were due to genetics and 53% environmental.

Biology and environment

“We know from previous research that around a third of people are at the higher end of the sensitivity spectrum. They are generally more strongly affected by their experiences,” said study leader Michael Pluess, a professor of developmental psychology at Queen Mary University of London.

“Because we now know that this sensitivity is as much due to biology as environment, it is important for people to accept their sensitivity as an important part of who they are and consider it as a strength, not just as a weakness,” he said in a university news release.

Pluess said this was the first time researchers have been able to quantify how much of the differences can be explained by genetics.

The study included more than 2 800 twins, 1 000 of whom were identical. Participants answered questions about how sensitive they were.

Shared genetic links

“If a child is more sensitive to negative experiences, it may be that they become more easily stressed and anxious in challenging situations,” said co-author Elham Assary, a postdoctoral researcher at Queen Mary.

“On the other hand, if a child has a higher sensitivity to positive experiences, it may be that they are more responsive to good parenting or benefit more from psychological interventions at school. What our study shows is that these different aspects of sensitivity all have a genetic basis,” she said in the release.

The researchers also looked at other personality traits, including openness, conscientiousness, agreeableness, extraversion and neuroticism. They found shared genetic links between sensitivity, neuroticism and extraversion, but not any other traits.

The findings were recently published in the journal Molecular Psychiatry.

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• There has been much debate over the years about the impact of coffee on human health 
• Caffeinated coffee, however, appears not to increase the risk of disease
• Moderation appears to be key, as caffeine is a stimulant and can make people jittery

Coffee has been tied to many potential health benefits, but people should drink it for pleasure, and not disease prevention.

That’s one of the main conclusions of a new research review. In it, researchers give an overview of the evidence on coffee and caffeine – the subjects of many health studies over the years.

“The impact of coffee consumption on health is important because there are few other dietary factors that so many people across the world are so frequently exposed to,” said Rob van Dam, the lead author on the review.

And overall, his team found, the news is good for coffee lovers: Caffeinated coffee does not appear to raise any disease risks, and is instead linked to lower odds of various diseases. And moderate doses of caffeine are generally safe for most people.

Pregnant women should be careful

“Moderate” is the key, however. Too much caffeine can disrupt sleep or make people jittery.

“The amount of caffeine that leads to unpleasant side effects varies greatly from person to person,” said van Dam, a professor at the National University of Singapore.

He suggested people pay attention to whether caffeine seems to affect their ability to fall asleep or lead to “agitation or anxiety”. If it does, van Dam said, “they can adapt their level of intake or timing of intake during the day.”

That’s the advice for most adults. Pregnant women, however, should be particularly careful about caffeine intake. Based on the evidence, van Dam’s team said, they should limit themselves to no more than 200 milligrams of caffeine a day.

That’s roughly the amount in 12 ounces of coffee.

For non-pregnant people, van Dam said that up to five 8-ounce cups of coffee a day may be fine, depending on a person’s caffeine tolerance.

Much back-and-forth

Lauri Wright is chair of nutrition and dietetics at the University of North Florida, and a spokesperson for the Academy of Nutrition and Dietetics.

“There’s been so much back-and-forth over the years about whether caffeine is good or bad,” said Wright, who was not involved in the review. “So it’s good to come back to the evidence.”

In general, studies show that despite caffeine’s bad reputation as a stimulant, caffeinated coffee does not seem to raise the risk of developing high blood pressure – or worsen existing blood pressure problems.

In fact, coffee consumption has been linked to lower risks of developing heart disease, as well as other serious conditions. The list includes type 2 diabetes, certain cancers, Parkinson’s disease, liver disease and gallstones, according to the review.

None of those studies, however, proves that coffee – or caffeine – is responsible for the lower risks, Wright said. She agreed with the report’s conclusion that people should not rely on java to prevent any diseases.

“But coffee and caffeine can be part of a healthy lifestyle,” Wright said.

Energy drinks the exception

There is a question over whether filtered coffee (from a drip coffee maker, for instance) is healthier than unfiltered. The latter includes espresso, boiled coffee and coffee made by French press, for example.

According to van Dam, research shows that unfiltered coffee can raise blood cholesterol levels.

Wright, however, said, “What you put into the coffee is what really matters, rather than whether it’s filtered or unfiltered.” That is, avoid loading that coffee cup with sugar and cream.

“Some of these coffee drinks people buy are more like milkshakes,” Wright said.

There are other sources of dietary caffeine, including tea, sodas and chocolate. For the most part, though, they contain low amounts, Wright said.

Two exceptions, she noted, are energy drinks and “shots”, which can contain as much or more caffeine than a cup of coffee. High intake of those beverages can cause spikes in blood pressure and heart palpitations, according to the review.

Caffeine can also interact with certain medications. If people have questions about their medications, Wright said, they can talk to their pharmacist.

The review was published on 23 July in the New England Journal of Medicine.

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