A study looked at the hobbies of a group of people with Alzheimer's, compared to a healthy group.
Dr Robert Friedland said watching TV was the only recreational activity, out of those studied, that Alzheimer's sufferers were more likely to participate in.
But Dr Richard Harvey, director of research from the Alzheimer's Society said the US research did not prove there was any link.
 Of all the activities we quantified ... Alzheimer's patients are in middle life less active in all of them - except for one, which is television  |
Dr Robert Friedland, Alzheimer's researcher |
Alzheimer's affects over 700,000 people in the UK. One in 20 between 70 and 80 and one in five over 80 have the condition.
The most common symptoms are memory, speech and perception problems.
'Less active'
Dr Friedland led the team of researchers from the Case Western Reserve University Hospital of Medicine and the University Hospitals of Cleveland.
The researchers looked at three kinds of activity - passive, intellectual and physical - covering all kinds of ways people spend their time outside work, from visiting friends to playing an instrument and sports.
There have been a lot of studies in the past that have shown an association between physical and mental activity and a reduced risk of Alzheimer's |
Dr Richard Harvey, Alzheimer's Society |
Dr Friedland said: "The brain is an organ like any other organ which ages in regard to how its used. So learning is important for the brain - that's the purpose, like the heart pumps and the muscles constrict.
"The brain has been honed by evolutionary forces to be active, and learning is an important part of life.
"When you watch TV, you can be in a semi-conscious state where you really are not doing any learning."
The study, published in the Proceedings of the National Academy of Sciences, suggested that people who were relatively inactive had a 250% increased risk of developing Alzheimer's.
It surveyed the carers of 193 Alzheimer's patients and 358 of their healthy friends, neighbours and acquaintances, and quizzed them about their different hobbies in middle-age.
It found those with Alzheimer's were less likely to have had intellectual hobbies, and were unlikely to have had as wide a range of interests as their healthy peers.
Dr Harvey told BBC News Online Alzheimer's Disease was a complex condition, and that its cause was unlikely to be as simple as watching TV.
He added that as the researchers had asked carers for the group with Alzheimer's about their habits rather than the patients themselves the data was likely to be inaccurate.
Carers were more likely to remember periods of inactivity, he said.
In contrast, he said the healthy people taking part could have been more likely to exaggerate the amount of physical activity they undertook.
Dr Harvey added that there was no direct cause identified for what was a complicated condition, but added: "There have been a lot of studies in the past that have shown an association between physical and mental activity and a reduced risk of Alzheimer's."
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