Your secret strength-building weapon could be sitting in your medicine cabinet. Upping your intake of vitamin D may help you maintain stronger muscles, says recent research published in the journal Medicine & Science in Sports & Exercise.

Researchers examined 419 adults (20 to 76 years old), and after controlling for multiple factors like age, gender, body mass index, and blood pressure, found that the participants with higher levels of vitamin D in their system had a stronger association with arm and leg strength. (There was a more consistent link between D levels and arm strength.)

Even though vitamin D’s usual claim to fame is its role in helping your bones absorb calcium, the researchers say that vitamin D also plays a crucial role in developing your Type II skeletal (a.k.a. fast-twitch) muscle fibres. As for why the vitamin may have more of an effect on your upper body, researchers chalk it up to the differences in fibre type composition between the arms and legs.

So how much of this vital vitamin should you be downing a day? The Institute of Medicine recommends a dietary intake of 600 IU per day, which is the equivalent of 3 ounces of cooked salmon and 3 ounces of canned tuna. Not a huge fan of fish? Eggs, fortified milk, and cereals are other good sources of Vitamin D.