Estas biendeando mal los datos, intenta algo así.
Código PHP:
require_once('conexion.php');
$conexion = conectar();
$id = $_GET["id"];
$sql = "SELECT EMAIL FROM USUARIO WHERE ID = :i";
$statement = $conexion -> prepare($sql);
$statement -> bind_param(":i", $id);
$statement -> execute();
$statement -> bind_result($email);
$statement -> fetch();
$statement -> close();
if(isset ($email)){
$sql = "UPDATE USUARIO SET ESTADO = 1 WHERE ID = :i";
$statement = $conexion -> prepare($sql);
$statement -> bind_param(":i",$id);
if($statement -> execute()){
echo "Bien";
}
$statement -> close();
}
$conexion -> close();