The company explains on its blog:

"To uncover the key to sickness and recovery, we looked at anonymized data from Jawbone's fitness tracker and UP App, in particular, user comments on their own activity that included words related to flu. We computed a sickness likelihood score as the change in the fraction of flu related comments over the normal baseline and studied how this score varied with seasons and demographic factors."

Based on users' self-reported BMI, the study clearly showed that overweight and obese users were far more likely to catch the flu. For adults ages 18-54, those classified as "very severely obese" were more than twice as likely to get sick as those whose weight was classified as healthy.

Those classified in the two less extreme obesity categories–moderately or severely obese–were also significantly more likely to get the flu than those of a healthy weight.

But the greatest predictor of flu sickness was not weight but walking patterns.

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Those who took more than 14,000 steps a day were four times less likely to get the flu than those who took less than 4,000 a day.

In the middle of the pack, those who took more than 8,000 but less than 10,000 steps were still nearly three times less likely to get sick than those who walked the least.

And they were about 50 percent less likely to get sick than those who walked between 4,000 and 6,000 steps a day.

While it's not surprising that those who are up and about more are less sick, the study does not provide evidence of causation. Some may walk less as a result of pre-existing illness or disabilities.