As awful as sitting all day can be for your health, it turns out standing for a long time may be even worse.

People with jobs that require them to primarily stand — think retail sales clerks, cooks, bank tellers, waiters, gate agents, cashiers — are twice as likely to develop heart disease as people who spend their working day parked in a chair, a recent study published in the American Journal of Epidemiology found.

That may be happening because as you stand for hours at a time, blood pools in the legs, forcing your body to work harder against gravity to move it back up to the heart, increasing pressure in the veins, said lead author Peter Smith, a senior scientist at the Institute for Work & Health in Toronto. Over time, that can increase your risk of heart disease.

“If we can recognize that standing for a long period of time is just as bad for you, if not potentially worse, than sitting for a long period of time, maybe we should reconsider whether it’s worthwhile as a society to force certain occupations to stand for long periods of time,” Smith told TODAY.

There’s a public perception that if workers in these jobs are not standing, they’re not interested, he added.

The research involved more than 7,300 employed people who took part in the Canadian Community Health Survey. None had heart disease at the beginning of the study, but when researchers followed them over 12 years, the workers who were required to stand for long periods had double the risk of developing heart disease compared to their sitting colleagues.

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That risk stayed pretty much the same even when the researchers adjusted for age, education, marital status, BMI and health factors such as diabetes and high blood pressure.

The findings suggest standing on the job is an “often overlooked, cardiovascular risk factor” that should receive as much, if not more, attention than chronic sitting, the paper notes.

It's OK to stand on occasion

There’s little reason to worry if you’re using a standing desk at work, Smith said. That’s likely a choice, not a requirement, allowing you to sit down whenever you’re feeling tired.

“If you’re in an environment where you’re able to change body positions throughout the day, that’s positive,” he noted.

But if you’re sitting all day and think a standing break will provide a health benefit, don’t count on it. The energy you expend when you’re standing is not that different from sitting, Smith said. So while standing up for a while may help people with conditions like back pain, it won’t offset a sedentary lifestyle.

“The true opposite of sitting is actually to be more active; it’s not to stand,” Smith said.

What if you have to stand for work?

Prolonged standing on the job isn’t as common as sitting: Fewer than 10 percent of the people in the study had standing occupations, compared to about 37 percent who mostly sat at work. The rest of the participants had jobs that involved a combination of sitting, standing and walking.

If your job requires you to stand, try to sit down when you’re feeling tired, Smith advised. Employers should recognize standing for prolonged periods creates a health risk and offer that option, he added.

In general, moving every 30 minutes for at least one minute can reduce the health harms of too much sitting and sedentary behavior, and from any prolonged static posture at work, the author of a separate recent study advised.

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