TFA starts with "Vitamin D deficiency is widespread worldwide and is particularly common among cancer patients." and concludes "in the summary of the ten studi

TFA starts with "Vitamin D deficiency is widespread worldwide and is particularly common among cancer patients." and concludes "in the summary of the ten studies with daily dosing, the researchers determined a statistically significant twelve percent reduction in cancer mortality." So yes, not enough is bad, and many require supplementation to get to an ideal level. Nowhere was anyone proposing overdosing.