Maximise your muscle gains by keeping vitamin D levels topped up. Vitamin D deficiency has been shown to reduce strength, type two fast twitch muscle fibres and overall physical performance.3 Conversely, higher vitamin D levels have also been associated with healthier body composition. While sunlight is the best source, you can also find vitamin D in oily fish like salmon and sardines, as well as egg yolks and oysters. Alternatively, get your levels checked and supplement with a vitamin D3 formula if needed.