Here is another product to boost your Vitamin D levels - all milk products have Vitamin D (including cheese and yoghurt) but what may help you, even more, is buying milk that has been fortified with Vitamin D. This is getting the best of both worlds - you are getting milk protein (one of the best proteins for muscle building), while also making sure you are not deficient in the essential Vitamin D. As an added bonus, you can also combine milk with oats to create some tasty oatmeal.