I Don't Give Medical Advise (anymore)
While in practice I tried to keep up with new discoveries in nutrition and diet and learned long ago that low vitamin D levels (common in northern latitudes) were associated with depression and may be part of the cause of SADs (seasonal affective disorder...treated with bright lights). I did blood levels on several patients who complained of depression and found low Vitamin D levels in their blood. On therapy their levels rose and so did their moods.
Now, a new study indicates that upping levels of Vitamin D helps treat (remove brain plaques) in Alzheimer's Disease. Perhaps that 5,000 units a day (which raised my levels to normal) is why my brain is so excellent at my age [(my wife (and others) would disagree].
Perhaps, too, it is the sun exposure and production of the vitamin that makes paddlers so happy. (BTW: Vit. D is fat soluble and requires some fat in the tummy to be absorbed well).
But you didn't hear it from me.