How the nose, eyes may hold early clues to Alzheimer's

Subtle shifts in our senses of sight and smell may offer early clues to Alzheimer's disease, before memory symptoms begin to surface, say researchers who presented new data at the Alzheimer's Association International Conference in Toronto this week.

It looks like "the eyes and the nose are a window to the brain," observed CBS News medical contributor Dr. David Agus.

One of the studies found that a thinning of the retinal nerve fiber layer in the eye tended to occur in people who performed more poorly in testing of cognitive skills like memory, reasoning and reaction time.

Agus, appearing on "CBS This Morning," said the finding makes sense. "If you look in the eye, the retinal nerve that comes out of the brain, if it gets narrower, that's an indicator of the onset of Alzheimer's."

Another study that focused on the sense of smell and involved a panel of 40 scratch-and-sniff surfaces scented with a range of familiar scents including turpentine, lemon, licorice, bubble gum and even "eau de skunk."

"If you can identify over 35 of them, you have a much lower chance of progressing to Alzheimer's. Below 35, it shows that it might be starting," said Agus.

It's not the sensitivity of the nose itself that diminishes, he pointed out. Rather, as cognitive impairment develops, the brain is less capable of identifying what those smells are.

The hope is that such tests could eventually lead to an easier way to accurately diagnose Alzheimer's early on -- a welcome alternative to having to undergo injections and imaging of the brain, including exposure to radiation.

Can you train your brain?

Another new study presented at the Alzheimer's conference focused on whether it's possible to ward off Alzheimer's by training your brain with a specially-designed computer game.

"This is a game where you either looked at memory, reasoning or processing. Speed processing -- if you did it for an hour for ten times -- decreased the incidence of Alzheimer's by over 30 percent over ten years. If you did a refresher at one and three years, [there was] a 48 percent reduction," said Agus about the research, dubbed the ACTIVE trial. "Those are dramatic numbers. We've never had a game that actually decreased dementia."

However, it's unclear whether these promising results will hold up under further testing.

"We just don't know. And it's not taking people in this computer game study and reversing [mental decline]," Agus clarified. "It's delaying the incidence, which is just as good as a win in these cases. Obviously, all of us want to delay this horrible disease that steals the soul."

But Hilda Bastian, a blogger for the PLOS Blogs (PLOS is a peer-reviewed scientific journal) argues that claims about the benefits of the brain training game are being blown out of proportion with sensational headlines.

"It's just a few months since the US Federal Trade commission fined a company $2 million for false advertising based on brain training claims like this. And in October 2014, an international scientific consensus statement tried to stem this tide. Yet here we are again," she wrote.

Bastian noted that the study has not yet been peer-reviewed or published in a scientific journal -- it's only an abstract that was presented at the Alzheimer's conference, so other researchers have not had the opportunity to vet the data.

"Details that come out about trials later are often quite different to what was presented at conferences," she explains. "A study of cardiology articles post-conferences from 1999-2002 found around 40 percent had discrepancies, and a sports medicine study found 63 percent had at least one major issue. And the day before this ACTIVE trial hype landed, I had tweeted about a study that probably has the record on these discrepancies: 96 percent - plastic surgery FTW!"

Bastian, also the chief editor of PubMed Health, part of the U.S. National Library of Medicine (though she notes that her PLOS blog is based solely on personal opinion), questioned the methodology used in the trial, too.

"The trial was not set up with methods designed to be able to answer the question about an effect on dementia," she wrote. "As the trial progressed, with little impact being found, the trial was modified -- trying to boost the impact."

Growing problem of Alzheimer's

About 5.4 million people in the U.S. have Alzheimer's -- one in nine people age 65 and up -- and it's the sixth leading cause of death, according to the U.S. Centers for Disease Control and Prevention and the Alzheimer's Association.

Agus said he's hopeful, though, that research is moving in the right direction and we'll one day be able to beat the disease.

"I'm an optimist. I see what's going on. For the first time now, we have drugs in development that are hitting the biologic processes involved in Alzheimer's. And so there is a lot of excitement there," he said.

What else can people do to reduce the risk of developing Alzheimer's?

"We can be lean -- body mass. We can exercise. We can take care of our blood vessels. We can do all of the things that have been shown or possibly associated [with reducing risk]. But I'm really optimistic because some of the drugs in clinical trials now, I think are going to show benefits."