Several studies show that vitamin D supplementation has huge benefits for any and everyone. It has been shown to be anti-estrogenic (specifically in fat cells, hell yah), raise testosterone levels, helps people lose fat faster, lengthens life span, increases strength levels and many other PROVEN benefits.
Check out Ergo-log for studies on vitamin D. Very interesting stuff. It's definitely my number 1 supplement.
I also wonder about the differences, however, in sun vs. vitamin D supplements. To get vitamin D you need a certain natural oil that your skin produces to be coating your skin. If you've been swimming it's likely that oil is not in abundance. Also, prolonged sun exposure eventually stops producing vitamin D whereas obviously supplementation you can control exactly how much vitamin D you're taking in.