Seasons May Tweak Genes That Trigger Some Chronic Diseases : Shots - Health News Genes linked to inflammation are more active in winter, a study hints. That might partly explain why some diseases, including Type 1 diabetes and rheumatoid arthritis, are more likely to start then.

Seasons May Tweak Genes That Trigger Some Chronic Diseases

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MELISSA BLOCK, HOST:

The seasons can affect all sorts of things - the weather, the length of the day and our DNA. That last one comes out of some surprising new research. NPR health correspondent Rob Stein has the details, and he couldn't get a certain song out of his head all day.

ROB STEIN, BYLINE: Scientists know the time of day can be a big deal for our bodies, determining when we should sleep, when certain hormones spike, and poets and musicians have long mused about the role the seasons play in our lives.

(SOUNDBITE OF SONG, "TURN! TURN! TURN!")

THE BYRDS: (Singing) To everything - turn, turn, turn. There is a season - turn, turn, turn.

STEIN: Doctors have known for a longtime that certain diseases are more likely to occur during certain seasons than others, but John Todd of the University of Cambridge says no one ever knew why.

JOHN TODD: Certain chronic diseases are very seasonal, like seasonal affective disorder or cardiovascular disease or Type 1 diabetes or multiple sclerosis or rheumatoid arthritis. But people have been wondering for decades what the explanation for that is.

STEIN: So Todd and his colleagues decided to try to find out. They took a look at our DNA to see if the seasons influence our genes. They analyzed the genes and cells for more than 16,000 people in five countries and report what they found in the journal Nature Communications.

TODD: We find that a quarter of the genes in the human genome - so 4,000 genes - their pattern of activity differs according to season. It's one of those observations where you - the first time you see it you go wow, somebody must have seen this before.

STEIN: But Todd says no one had. And when the researchers looked more closely at which genes were more or less active during some seasons than others, one big thing jumped out.

TODD: One of the standout results were that genes promoting inflammation were increased in winter, whereas genes suppressing inflammation were decreased in the winter. So overall, it looked as if this gene activity pattern really goes with increased inflammation in the winter.

STEIN: And inflammation, which is caused by the immune system getting out of whack, has long been associated with many of those health problems that spike in the winter. Now, Todd says no one knows how the seasons affect our genes, but there are some obvious possibilities.

TODD: As the seasons come on it gets colder, the days get shorter, so daylight and temperature could be factors.

STEIN: Other researchers say the findings could have far-reaching implications. Akhilesh Reddy studies the human body clock at the University of Cambridge.

AKHILESH REDDY: The fact that they found so many genes that go up and down over the season is very interesting because we just didn't know that our bodies go through this type of seasonal change before. And if you look at the actual genetic evidence for the first time, this is pretty profound really.

STEIN: Reddy thinks the findings would triggers scientists to start looking for other ways the seasons may have power over people's bodies.

REDDY: People might have a variation in their responses to all sorts of things that we haven't really thought about yet. You know, your drug responses might vary through the years. Even your cognitive performance - you know, we talk about exams and things like that - might be influenced subtly by the time of the year at which you're assessed. There's never been a marker before that you can look in the blood or whatever to say you're looking like you're a winter person now versus a summer person.

STEIN: So it could be the artists and musicians were right about the seasons after all.

(SOUNDBITE OF SONG, "TURN! TURN! TURN!")

THE BYRDS: (Singing) A time to be born, a time to die; a time to plant, a time to reap.

STEIN: Rob Stein, NPR News.

(SOUNDBITE OF SONG, "TURN! TURN! TURN!")

THE BYRDS: (Singing) A time to heal, a time to laugh, a time to weep. To everything - turn, turn, turn. There is a season - turn, turn, turn. And a time to every purpose under heaven...

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