They are saying that fully formed vitamin A(retinol)either from natural cod liver oil or from pills in large amounts can block vitamin D, but that the studies showed the effect doesn't happen with beta carotene.

Many studies showed that up to 20,000 IU a day can be taken by a 150 pund person without a chance of toxicity, however the more recent studies showed negative effects on vitamin D levels at lower levels than this of vitamin A. i just decreased my vitamin A intake to 10,000 IU a day, and plan to get some carotene supplements. I might decrease the retinol further after that. I am afraid to stop taking retinol completely(in case my body isn't converting at least some carotene to retinol).