The 21-year-old defender joins fellow new signings Alex Pritchard, Corry Evans, Callum Doyle and Dennis Cerkin in moving to Wearside this summer.
Alves is the second loanee at the club this year, with fellow centre-back Callum Doyle on loan at the Stadium of Light from Manchester City.
The Denmark under-21 international joined West Ham in January from Danish side Silkeborg IF after making 50 appearances in two and a half seasons.
Alves made 12 appearances for Hammers’ under-23 side after joining in January, he also made the bench for the first team on 13 occasions, although he did not make a senior appearance.
The youngster will hope to feature regularly for Lee Johnson’s side this season but has competition in Doyle, Tom Flanagan and Bailey Wright.
Should Cerkin, Doyle and Alves all line up together the combined age of the trio would be 57, meaning an average age of 19 which would represent a massive risk with a lack of first-team experience in their backline.
All three players are very highly rated, and that combination could well be seen from Sunderland at some stage this season.
When it comes to further additions, Sunderland are still believed to want another full-back on both sides as well as another striker, with some players currently at the club possibly making way to make room for those players in the squad.
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