Lead is a heavy metal that can have a laundry list of adverse effects when it accumulates in sufficient amounts in the human body. Lead damages the kidneys, central nervous system and can be especially hazardous to small children and pregnant women. As such, efforts have been made to eradicate lead from household products as much as possible.
The Food and Drug Administration (FDA) has expressed concern about frequent use of lead crystal glassware. It has specifically recommended that alcoholic beverages never be stored in lead crystal decanters for prolonged periods of time. The FDA has asserted that occasional use of lead crystal glassware does not correlate with adverse health outcomes, but its use should be limited.
There is some evidence that the amount of lead that can leach into liquid contained in a decanter or container can be reduced by soaking the lead crystal in vinegar for 24 hours when the piece is first acquired. The idea behind this practice is that any loose lead molecules on the glass will be leached into the highly acidic vinegar, which can then be safely dumped to reduce future leaching into beverages.
Even with older pieces, it is good practice to rinse out lead crystal decanters and glassware with water prior to filling them. Loose lead can remain in decanters and continue to leach from the lead crystal for decades after manufacturing. A quick rinse may help reduce your exposure to lead as will limiting your use of lead crystal to special occasions.