From CardioSmart
Announced at American Heart Association Scientific Sessions in Dallas.
The DAYLIGHT Study (Vitamin D therapy in individuals at high risk of hypertension), was stopped after 6 months with 4,000 IU of vitamin D when there was no reduction in blood pressure.
For many people who are very vitamin D deficient a constant dose of 4,000 IU takes many months to restore vitamin D levels.
Suspect that the trail was stopped just when vitamin D levels could start reducing blood pressure.
See also VitaminDWiki