Everyone who has an office job is likely to suffer vitamin D deficiency. Besides, prolonged exposure to the sun can lead to skin cancer, and balancing the exposure needed for vitamin D while minimizing the risk of skin cancer is difficult. That's why doctors usually prescribe vitamin D supplement when deficiency is found. Of-course, the level of vitamin D in the blood needs to be monitored and adjusted as any vitamin overdose is also risky.
So once again, we have a hype over nothing, and gaming is yet again blamed for problems it's not actually responsible for, by some conservative smart-ass.
Sure, doing nothing but playing video games all day can cause lots of problems, but that's just the result of over-doing something.
You can over-work, over-drink (not just alcohol, but water too), over-eat, over-exercise, over-medicate, over-expose yourself to the sun or to cellular phones radiation, etc. ...
All those things will have negative consequences.
Moderation and balance is the only way to healthy living, really.