Dr John Cannell at the Vitamin D Council did a thorough review of the literature and found that 10,000 IU of Vit D3 is safe for long-term supplementation. The skin can make that much Vit D after a relatively short exposure to the sun (well before it turns pink). In some parts of the world (such as the UK), local atmospheric conditions absorb significant amounts of UV light, so even being outside in the sun isn’t a guarantee of having enough Vit D.
It’s not uncommon these days for people to need one to three months of 50,000 IU/day to get their levels corrected. Always take Vit D3, not D2, and take it in the morning. Bio-Tech is a good brand; they are a high-quality manufacturer. I’ve used them for years, and have followed-up with lab tests to verify levels, with excellent results.