Story highlights Sanders is the oldest candidate in the presidential field who would be the oldest president to take office

The announcement comes after a Clinton-aligned super PAC suggested it would call on the 74-year-old Vermont senator to verify his health

Charleston, South Carolina (CNN) Bernie Sanders will release a letter from his doctor before the Iowa caucuses on February 1, his campaign manager said Saturday.

The announcement comes after a Clinton-aligned super PAC suggested it would call on the 74-year-old Vermont senator to verify his health, and one day before the fourth Democratic debate, held in Charleston, South Carolina.

The letter, Jeff Weaver said, would prove Sanders -- the oldest candidate in the presidential field who also would be the oldest president to take office -- is in "excellent health."

The Sanders campaign's decision came after David Brock, the head of a Hillary Clinton super PAC able to coordinate with the campaign, telegraphed his plans to call for the medical records this weekend here.

Politico first reported Brock's plans, and a source with knowledge of his plans confirmed his desire to call for the records in a conversation with CNN on Saturday. Brock, who once was a Clinton antagonist, is now a vocal Clinton defender and surrogate.

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