Many MeSH terms haven’t been part of the vocabulary for the entire history of MEDLINE. In addition, as MeSH changes, records previously indexed are not re-indexed. This means that any time you see dates at the top of the MeSH Database record, the term can only retrieve records indexed during a specific time period.

For example, see the MeSH Database record for the term Jet Lag Syndrome:

This term was introduced in the year 2000. This means that the only records in MEDLINE with this term applied were indexed in 2000 or later. To find literature about jet lag that was indexed prior to 2000, look for terms suggested under Previous Indexing on the MeSH Database record:

If no Previous Indexing term exists for a term, use the next broader term(s) in the MeSH hierarchy.

To limit your search to the time period of interest, you can specify the indexing date range using the search tag [mhda]. For example, to search for MEDLINE records indexed with Sleep Disorders between 1974 and 1999, you can search:

Sleep Disorders[mh] AND 1974:1999[mhda]

Because earlier literature was probably indexed with less specific terminology, you may want to add keywords to your search to narrow to records of interest. For example:

Sleep Disorders[mh] AND 1974:1999[mhda] AND (jet lag OR travel)

[NOTE: This search is used to demonstrate search mechanics and has not been tested for sensitivity or specificity. Please consult an experienced searcher at your health sciences library for guidance.]