If your performance is hitting a plateau, and protein isn’t a problem, you might be short on vitamin D. An International Journal of Sport Nutrition and Exercise study found that athletes sapped of the vital nutrient didn’t measure up to their powered-up peers.

Looking for a vitamin D boost? Supplements will do the trick, but one of these will make a meal of it:

1. Salmon

Oily or fatty fish is generally acknowledged as a great source of Vitamin D – although a recent study in The Journal of Steroid Biochemistry and Molecular Biology showed that farmed salmon can contain a fraction of the Vitamin D content of the wild variety. Point being: go wild.

2. Cod Liver Oil

A tablespoon a day will keep all kinds of bad things away: high blood pressure, kidney disease, high cholesterol – even depression. More than that, and you’re actually at risk of overdosing on Vitamin D. (Given the taste, though, we’re not sure you’d be able to force down more than a Tbsp anyway.)

3. Sunshine

As if you needed another reason to get that shirt off on the beach – sure, it will get you noticed, but it’ll also increase your intake of Vitamin by up to 1 000%. A study in the Journal of Pharmacology and Pharmacotherapeutics suggests hitting beach between 10am and 3pm to load up on the so-called “sunshine vitamin”.