Atheists consistently rank among the lowest of the low in the court of American public opinion. Now, research suggests one reason why: Thinking about atheists reminds people of death.

In fact, prompting people to think about atheism triggered death-related thoughts just as strongly as, well, directly prompting people to think about death, a new study finds. These death thoughts help trigger a subconscious dislike of atheists, said study leader Corey Cook, a social psychologist at the University of Washington, Tacoma. Not only do thoughts of death put people in a negative frame of mind, Cook told Live Science, but they also prompt people to hold more tightly onto their own values.

"There's a little circular thing going on where encountering atheism will make people grasp their values closer and then become more negative because atheists are perceived as not having values," Cook said. [8 Ways Religion Impacts Your Life]

Anti-atheist prejudice

Atheists in America have an image problem. Studies and surveys consistently rank nonbelievers as untrustworthy, threatening and un-American. Researchers reporting in a 2011 paper published in the Journal of Personality and Social Psychology even found that people viewed atheists as equally untrustworthy as rapists.

This previous work found that atheists are perceived as without morals and values, Cook said. Intriguingly, people's values are closely tied up with people's feelings about death. When people are reminded of their own impending deaths, they become more protective of their worldviews and show increased prejudice against those with different worldviews. [Saint or Spiritual Slacker? Test Your Religious Knowledge]

As such, Cook's co-author, Sheldon Solomon of Skidmore College in New York, reasoned, if atheists threaten believers' values, they should also prompt thoughts of death.

The researchers joined with Florette Cohen at the College of Staten Island CUNY to survey a diverse group of students at that school in order to test the idea. First, 236 students were asked to sit down and write about either thoughts of their own deaths or thoughts of being in extreme pain. After a few distraction tasks, the students next answered questions about their feelings toward either atheists or Quakers (a Christian religion). About 65 percent of the participants were Christian, while the rest were Muslim, Buddhist, Jewish or another faith.

Story continues

Overall, people viewed atheists much more negatively than Quakers, Cook said. But when prompted to think of death, people became even more negative toward atheists, while their attitudes toward Quakers didn't budge. They trusted atheists less, reported fewer warm feelings toward them, and felt more prejudice, the researchers reported in the journal Social Psychological and Personality Science.

Death and belief

In a follow-up experiment, the researchers flipped the script. Instead of nudging people to think about death to see how that changed their views on atheism, they had people think about atheism and then tested the effect on thoughts of death. Two hundred students of various religious faiths first wrote about their thoughts on their own deaths, on atheism, or on experiencing extreme pain. Next, they did a word-completion task where they were given prompts like "S K _ _ L," which could spell out a neutral word (skill) or a death-related word (skull).

The people prompted to think about death were more likely than those prompted to think about pain to complete the words with death-related options, unsurprisingly. But more shocking was that the people who thought about atheism were just as likely as the people who thought about death to pick death-related answers.

"We found that thinking about atheism actually increased thoughts of death to the same extent as thinking about death itself," said Cook, who described the result as "surprising."

Atheists may cue thoughts of death because they threaten people's vision of the afterlife, the researchers wrote. When these central values about life after death are threatened, people cling to them more tightly and reject those who don't share them.

An important next step in the research, Cook said, is to figure out how to lessen the perceived threat, and, in turn, reduce prejudice. Research on stereotypes and prejudice suggests changing such perceptions is very difficult to do, he said, but part of the answer is likely to make atheism more visible in daily life. Many people think of inflammatory personalities such as Christopher Hitchens or Richard Dawkins when they think of atheists, Cook said.

"Those who are vocal tend to be pretty extreme, and unfortunately I think they drive the perception of what it means to be a nonbeliever or an atheist," he said.

Follow Stephanie Pappas on Twitter and Google+. Follow us @livescience, Facebook & Google+. Original article on Live Science.

Copyright 2015 LiveScience, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.