Upvote:2
The website you are quoting does not look very "official". The official website of Saint Lucia's customs department is www.customs.gov.lc
On that site you will find a list of the prohibited imports. Vitamins are not explicitly listed, but there is a forbidden item called "narcotic drugs". Depending on your "vitamins" an officer might consider them as narcotic drugs and confiscate them ... If you want to be sure, you can always try to contact the customs department.