I have had spider veins since I hit puberty (age 10), though luckily no varicose veins. When I was restricting my intake too much they were much much less noticeable, but I have no idea why.
At least I *think* they’re what you call spider veins. I googled spider veins and mine look less blotch-y/all-over-the-place and more like simple branches.
Sorry I can’t help with any suggestions, I’d love to know what causes them too.