Smoking and high blood pressure over the age of 50 both lead to accelerated mental decline, research has shown.
Scientists analysed risk factor data for more than 8,000 older adults taking part in the English Longitudinal Study of Ageing (Elsa).
Tests of memory, planning and overall mental ability were carried out after four and eight years.
The study showed that smoking consistently reduced all three performance measures after four years.
High blood pressure and high risk of stroke were associated with lower scores for memory and overall mental ability after eight years. Being overweight was linked to poor memory.
The findings appear in the journal Age and Ageing.
They indicate that future trials should focus on combinations of risk factors rather than individual causes of mental decline, say the researchers.
Lead scientist Dr Alex Dregan, from King's College London, said: "Cognitive decline becomes more common with ageing and for an increasing number of people interferes with daily functioning and well-being.
"Some older people can become forgetful, have trouble remembering common words or have problems organising daily tasks more than others.
"We have identified a number of risk factors which could be associated with accelerated cognitive decline, all of which, could be modifiable. This offers valuable knowledge for future prevention and treatment interventions."
The results indicate that high blood pressure has a gradual effect on the brain over a long period, according to the scientists.
This could explain why short-term trials of blood pressure lowering drugs being used to treat mental decline had failed to show a clear benefit.
Dr Dregan added: "Our research suggests that the most promising approach to delaying or preventing early ageing of the brain is one that acknowledges the multi-causality of cognitive decline."
Jessica Smith, from the Alzheimer's Society, said: "We all know smoking, a high blood pressure, high cholesterol levels and a high BMI (body mass index) is bad for our heart. This research adds to the huge amount of evidence that also suggests they can be bad for our head too.
"One in three people over 65 will develop dementia but there are things people can do to reduce their risk. Eating a balanced diet, maintaining a healthy weight, exercising regularly, getting your blood pressure and cholesterol checked and not smoking can all make a difference."
Dr Simon Ridley, from the charity Alzheimer's Research UK, said: "Research has repeatedly linked smoking and high blood pressure to a greater risk of cognitive decline and dementia, and this study adds further weight to that evidence. Cognitive decline as we age can develop into dementia, and unravelling the factors that are linked to this decline could be crucial for finding ways to prevent the condition."
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Catherine Zeta Jones
The Welsh actress, married to Michael Michael Douglas, reportedly quit her habit last year, while her husband struggled with throat cancer. The Chicago star was <a href="http://www.okmagazine.com/news/catherine-zeta-jones-trying-quit-smoking">snapped using an electronic cigarette</a> to help her fight her nicotine cravings.
The <a href="http://www.huffingtonpost.com/2012/08/12/jennifer-aniston-engaged-justin-theroux_n_1771083.html">recently engaged star</a> is <a href="http://www.elle.com/pop-culture/cover-shoots/women-in-hollywood-2011-605864#slide-1">no stranger to pregnancy rumors</a>. <a href="http://www.gq.com/entertainment/movies-and-tv/201203/jennifer-aniston-paul-rudd-gq-march-2012-cover-story">But she told GQ earlier this year</a> that one persistent baby rumor might have come after she kicked the cigarette habit. "Well, I recently quit smoking, and you do put on some extra pounds," she told the magazine. "It makes a difference, especially if you're not 20."
The POTUS, who started lighting up as a teenager, had a long battle with nicotine addiction. "I constantly struggle with it," he said in a 2009 news conference, <a href="http://www.huffingtonpost.com/2011/02/08/michelle-obama-president-_n_820340.html">HuffPost previously reported</a>. When he was first deciding to run for president, now first lady Michelle Obama said one of her requirements was that he kick the habit once and for all. And while he tried to quit during his 2008 campaign, it wasn't until 2011 that his wife broke the news that he had been smoke-free for a year, <a href="http://www.huffingtonpost.com/2011/02/08/michelle-obama-president-_n_820340.html">according to the HuffPost report</a>. Later that year, President Obama's doctor also confirmed that he successfully quit smoking, <a href="http://blogs.wsj.com/health/2011/11/01/obamas-doctor-says-hes-fit-for-duty-and-tobacco-free/?mod=WSJBlog&mod=WSJ_health">the Wall Street Journal reported</a>.
The model -- <a href="http://videos.huffingtonpost.com/entertainment/gisele-bundchen-confirms-pregnancy-517452968">who is pregnant with her second child</a> with husband and football star Tom Brady -- broke the habit in 2003. "When I quit smoking I gained 15 pounds," <a href="http://www.people.com/people/archive/article/0,,20059627,00.html">she told People magazine in 2006</a>. "So? I prefer myself this way. Nothing is worth your health."
For the actor, playing a chain smoker in Smokin' Aces was actually the impetus to give up the habit in real life. "The whole week that I shot, I smoked, like, five packs a day," <a href="http://www.people.com/people/article/0,,20010769,00.html">he told People magazine in 2007</a>. "By the time the movie was over, I was so sick of smoking, I just didn't want to do it anymore, and I quit. I have this celluloid record of the last time I smoked."
In May 2012, the Twilight actress <a href="http://www.mtv.com/news/articles/1686170/kristen-stewart-quits-smoking-learns-french.jhtml">revealed in an MTV interview</a> that she was learning French -- and that she had quit smoking! "You can't acknowledge it or else suddenly ... you can't think about it," she said shyly. And she's not the only Twilight starlet who's stubbed out her cigarettes -- co-stars Ashley Greene and Nikki Reed also reportedly stopped smoking, <a href="http://www.eonline.com/news/127306/which-new-moon-castmembers-are-trying-to-be-better-role-models">according to EOnline.com</a>.
"I was highly addicted," <a href="http://www.vogue.com/magazine/article/charlize-theron-breaking-away/#1">the actress told Vogue in 2011</a>. "I thought, I don’t smoke like normal people. I smoke to die." While Theron didn't tell Vogue exactly how she quit to avoid "jinxing" it, she reportedly tried both <a href="http://www.allaboutyou.com/health/health-advice/celebrity-ex-smokers-how-they-kicked-the-habit-46298?page=7">yoga</a> and <a href="http://www.huffingtonpost.com/2012/02/11/hypnosis-quit-smoking_n_1248444.html">hypnosis</a>.
The Mad Man star is no stranger to smoking on screen -- but he quit smoking behind the scenes at the age of 24, <a href="http://www.people.com/people/jon_hamm/0,,,00.html">according to People.com.</a> "It's glamorous on film, but it's not glamorous waking up and smelling like an ashtray," he told the publication. So how does he handle playing his chain-smoking character, Don Draper? Herbal cigarettes. "They taste like a mixture between pot and soap," <a href="http://www.vulture.com/2008/09/jon_hamm_on.html">he once complained to New York magazine's Vulture.com</a>. "But we’re being realistic -- people did smoke back then. My father smoked everywhere, even in the car, in the summertime, with the windows up -- it was part of life," <a href="http://blog.chron.com/celebritybuzz/2012/03/jon-hamm-smoking-onscreen-is-debilitating/">he told the Houston Chronicle earlier this year</a>.
The actress <a href="http://www.parade.com/celebrity/celebrity-parade/2010/1004-katherine-heigl-life-as-we-know-it.html">told Parade in 2010</a> that she was quitting with the help of electronic cigarettes, a <a href="http://abcnews.go.com/Technology/safe-cigarettes/story?id=12789204#.UH6c_xYiFsc">controversial smoking cessation tool</a>. "I've been doing it for six months. Smoking sucks! The one thing I would say to my kid is, 'It's not just that it's bad for you,'" <a href="http://www.parade.com/celebrity/celebrity-parade/2010/1004-katherine-heigl-life-as-we-know-it.html">she told Parade</a>. "'Do you want to spend the rest of your life fighting a stupid addiction to a stupid thing that doesn't even really give you a good buzz?'" Heigl told David Letterman that she had previously unsuccessfully tried the gum, the patch and the prescription drug Chantix to quit, <a href="http://www.huffingtonpost.com/2010/10/04/katherine-heigl-the-crazy_n_749616.html">HuffPost reported at the time</a>.