Dear Doctors: My husband caught a cold this summer, and he swears the readings from his fitness tracker a few days before warned him that he was about to be sick. Do you think that’s really possible?

Dear Reader: Your husband’s observations about how changes in the data from his fitness tracker preceded the onset of a cold actually dovetail with the findings of a study that were published at the start of the year. And it’s not the first research of its kind to make the connection. With millions of people now using fitness trackers, scientists are diving into the trove of uploaded data to see what the details may be able to reveal about public health.

For anyone unfamiliar with fitness trackers, they’re wearable sensors, much like a wristwatch, that measure a range of activity and health metrics. Depending on the device -- there are dozens of different brands and types -- fitness trackers measure steps taken, total mileage, speed, direction, elevation climbed and duration of activity. On the physiological side of things, they can track heart rate, heart rhythms, skin temperature and minutes of sleep. Some manufacturers even claim that, using motion sensors and algorithms, their models can map how long someone spends in the various stages of sleep. (Full disclosure: Many sleep specialists are skeptical about the accuracy of the sleep-stage results.)

In a recent study, researchers from the Scripps Research Translational Institute analyzed data collected from the fitness trackers of 47,000 adult women and men. Using a minimum of two months’ worth of readings taken over the course of two years, which included activity, heart rate and sleep, the researchers found that their predictions of regional flu outbreaks matched the statistical data collected by the Centers for Disease Control and Prevention during those same time periods. An earlier study, published by researchers at Stanford University in early 2017, had come to similar conclusions. In that study, the scientists collected 250,000 daily readings from just 43 individuals over the course of a year. The participants wore a range of biosensors, which collected information about daily activity, heart rate, oxygen saturation levels, skin temperature and sleep data. They even tracked exposure to radiation, such as the X-rays and gamma rays encountered in air travel.

As with the Scripps study, certain changes to the readings collected by the wearable sensors predicted coming down with a cold or the flu. These changes included persistent increases in resting heart rate, which were coupled with increases to daily sleep. One of the Stanford scientists, who was also a participant in the study, noticed he had an increased heart rate and a decrease in blood oxygen saturation. It turned out that he didn’t have a cold; instead, the data from the eight different biosensors he was wearing for the study led to an early diagnosis of Lyme disease, before any other symptoms of the condition had appeared.

It’s a fascinating line of inquiry that, no surprise, is getting additional study. In the meantime, listen to your body, stay home if you think you’re getting sick and, please, get your flu shot.

(Send your questions to askthedoctors@mednet.ucla.edu. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctors: I used to be pretty active, but after a diagnosis of Afib in the spring, I’ve become reluctant to exercise. My wife is after me to get moving again, and my son says he just read that people with Afib live longer if they exercise. Is he right?

Dear Reader: Your son appears to be up on the latest research regarding people living with the heart condition known as atrial fibrillation, also referred to as Afib or AF. We’ll get to that in a moment, but first, the basics. Afib is a common heart rhythm problem, or arrhythmia, in which the upper chambers of the heart aren’t behaving properly. Instead of beating in a regular and predictable fashion, the upper chambers, which are called atria, quiver and fail to coordinate with the lower chambers of the heart, known as ventricles. This results in a chaotic and disorganized heartbeat, which interferes with the efficient and orderly flow of blood through the heart. Afib can also lead to the formation of blood clots, which increases the risk of stroke.

For some people, Afib has no discernable symptoms. They may only become aware of the condition when it’s discovered during a routine doctor’s visit. Others can feel physical sensations, such as an irregular heartbeat, skipped beats or a racing heart. Afib can cause someone to feel dizzy or lightheaded, have chest pains and experience shortness of breath or fatigue that is out of proportion to their exertions.

Treatment typically includes medication to control the heart rate, blood thinners to guard against stroke and lifestyle changes to manage risk factors. Those risk factors include obesity, high blood pressure, diabetes, alcohol use, smoking and hyperthyroidism. Advanced age and certain existing heart problems also raise the risk of developing Afib. In some cases, surgery to shut down the area of heart tissue that is dictating the rogue heartbeat may be recommended.

It’s not surprising that, when diagnosed with any type of heart problem, someone might be leery about exercise and exertion. However, a study published earlier this year in the European Heart Journal had good news. Researchers who studied 1,100 people living with Afib over the course of nine years found that individuals who got regular exercise were 45% less likely to have died at the end of the study period than those who remained sedentary. It’s important to note that, while observational studies like this can pinpoint a certain outcome, they can’t establish the reason it was reached. Exercise was a common factor among the people who lived longer, but the study can only suggest it as a factor in their longevity, and not decisively prove it.

Still, a wealth of existing research links exercise with lower blood pressure, improved blood lipid levels, better blood glucose management and weight control -- each a risk factor in Afib. Our advice is to listen to your family and get moving again. Check in with your health care provider, share your worries, and together you can craft an exercise plan that’s safe and appropriate.

(Send your questions to askthedoctors@mednet.ucla.edu. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctors: My husband and I were shocked when our nephew was diagnosed with colon cancer. He’s only 36 years old. Isn’t that awfully young? It seems like we’re hearing about a lot of younger people getting this kind of cancer. Why is this happening?

Dear Reader: Unfortunately, you’re correct about the increase in the number of younger adults being diagnosed with colon cancer at this time. And with the recent death of actor Chadwick Boseman from the disease, the disturbing trend has entered the national consciousness. Excluding skin cancers, cancers of the colon and rectum -- collectively referred to as colorectal cancer -- are the third most commonly diagnosed types of cancers that occur in both men and women in the U.S. They account for more than 50,000 deaths each year.

Until recently, colon cancer was not prevalent among younger adults. This had been reflected in the screening guidelines put forth by the American Cancer Society, which had recommended that regular screenings for colon and rectal cancers begin at age 50. But statistics show that younger adults are increasingly affected by this type of cancer. Of the estimated 135,000 cases of colorectal cancer predicted for this year, at least 12% will be discovered in people younger than 50.

As a result, the screening guidelines have since been updated. It’s now recommended that regular screenings should begin at age 45. Individuals living with inflammatory bowel disease, and those with a family history of it, are at increased risk of colorectal cancers. They may be advised to start screenings even earlier.

Screening for the disease includes colonoscopies, which are used to identify and, when possible, remove polyps and other growths. Fecal tests can be useful in identifying blood in the stool. Each of these can be indicators of cancer or a pre-cancerous condition. A study published last year found the updated age guidelines for colorectal cancer screenings can prevent about 30,000 potential cases each year and save 11,000 lives. Not all insurance companies are on board with the new guidelines, though, and some patients would have to pay for earlier screenings themselves.

As for why the disease is striking an ever-younger population, researchers still aren’t sure. Some suspect changes to behavior, as well as environmental factors, and have launched studies to learn more. Others worry that younger adults are ignoring the physical symptoms that may indicate the presence of colorectal cancer. These include visible blood in the stool, particularly when it’s bright red in color; rectal bleeding; persistent sensations of pressure within the bowel and abdomen that are not relieved by a bowel movement; ongoing abdominal pain and cramping; weakness or fatigue and unexplained weight loss. Another indicator is changes to bowel habits that last more than a few days, such as constipation, diarrhea or a change to the shape of the stool. If anyone experiences one or more of these symptoms, it’s important to check in with your health care provider. The good news is that, when caught early, colorectal cancers are highly treatable.

(Send your questions to askthedoctors@mednet.ucla.edu. Owing to the volume of mail, personal replies cannot be provided.)