Did you know that the maximum amount of air healthy adult lungs can hold—also called total lung capacity or TLC—is about 6 liters? That is about three large soda bottles.

Your lungs mature by the time you are about 20-25 years old. After about the age of 35, it is normal for your lung function to decline gradually as you age. This can make breathing slightly more difficult as you get older. If you notice any sudden difficulties in breathing or shortness of breath, talk to your doctor right away. This could be a sign of lung disease and not the normal process of aging.

There are several natural body changes that happen as you get older that may cause a decline in lung capacity. Muscles that assist with breathing such as the diaphragm can get weaker. Lung tissue that helps keep your airways open can lose elasticity, which means your airways can get a little smaller. Your rib cage bones can change and get smaller which leaves less room for your lungs to expand.

A decrease in lung function is a normal part of the aging process but there are steps you can take to stay as healthy as possible. Staying active, avoiding tobacco smoke and stay up to date on vaccinations are just a few ways you can protect and even strengthen your lungs.

Following all of these simple tips will help you continue to breathe well throughout your lifetime.

Spirometry is a diagnostic test that provides different measures of lung capacity. Often used to diagnose chronic obstructive pulmonary disorder (COPD) or asthma, spirometry results are also used to see if your breathing has improved after treatment for a lung condition.

Some examples of spirometry measurements are:

Forced vital capacity: the maximum amount of air you can forcibly exhale from your lungs after fully inhaling. It is about 80 percent of total capacity, or 4.8 liters, because some air remains in your lungs after you exhale. Forced vital capacity can decrease by about 0.2 liters per decade, even for healthy people who have never smoked.

Forced expiratory volume (FEV1): the amount of air you can exhale with force in 1 second. FEV1 declines 1 to 2 percent per year after about the age of 25, which may not sound like much but adds up over the course of a lifetime.

Learn more about when spirometry is needed, how it’s performed and understanding results.