Supplements may help
Although there is not all that much vitamin D in our diet, the better sources include oily fish and egg yolks. Another option is to take a supplement like BioActive D-Pearls that contains biologically active vitamin D3 in oil. This formula has extremely good bioavailability, according to published studies. One study was conducted on young school pupils and looked at vitamin D levels and mental performance, while the other study was carried out on athletes and looked at muscle function.