Nigel,

I had my PCP run a full work blood panel on me, and Vitamin D was low. So I've added 4000 IU Vit D daily. It seems to have helped with cognitive task.

I always love the medical advice:
PWP tend to have low Vitamin D, so spend more time in the sunshine.
PWP tend to have higher incidents of Melanoma (skin cancer) so be sure to stay out of the sun, or use lots of sun block.