MySQL Join Inconsistent Performance Depending on WHERE - mysql

Question

I have a query that is taking several seconds to complete for certain WHERE conditions. To the best of my knowledge, everything is indexed correctly, but performance is still poor. All tables are InnoDB, blog_users and blog_users_profiles contain about 5 million rows and forum_contacts has about 10K rows.
The query
SELECT blog.*
FROM blog_users AS blog
INNER JOIN blog_user_profiles AS profile ON blog.user_id = profile.user_id
INNER JOIN forum_contacts AS contact ON profile.forum_id = contact.user_id
WHERE blog.comments > :comment_cutoff
AND blog.last_active > :time_cutoff
AND contact.type = :contact_type
AND contact.area = :location
LIMIT 0, 100
Explain output
+----+-------------+---------+--------+------------------------------+-----------+---------+------------------------------+---------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+---------+--------+------------------------------+-----------+---------+------------------------------+---------+-------------+
| 1 | SIMPLE | blog | range | PRIMARY,last_active,comments | comments | 3 | NULL | 1313813 | Using where |
| 1 | SIMPLE | profile | eq_ref | PRIMARY,forum_id | PRIMARY | 3 | xc_db.blog.user_id | 1 | |
| 1 | SIMPLE | contact | eq_ref | PRIMARY,type,area,user_id | PRIMARY | 80 | xc_db.profile.forum_id,const | 1 | Using where |
+----+-------------+---------+--------+------------------------------+-----------+---------+------------------------------+---------+-------------+
Table structure (irrelevant rows snipped)
blog_users
+-------------+-----------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+-----------------------+------+-----+---------+----------------+
| user_id | mediumint(8) unsigned | NO | PRI | NULL | auto_increment |
| username | varchar(16) | NO | UNI | NULL | |
| comments | mediumint(7) unsigned | NO | MUL | NULL | |
| last_active | int(10) unsigned | NO | MUL | NULL | |
+-------------+-----------------------+------+-----+---------+----------------+
blog_user_profiles
+----------+-----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+-----------------------+------+-----+---------+-------+
| user_id | mediumint(8) unsigned | NO | PRI | NULL | |
| forum_id | mediumint(8) unsigned | NO | MUL | 0 | |
+----------+-----------------------+------+-----+---------+-------+
forum_contacts
+---------+-----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-----------------------+------+-----+---------+-------+
| user_id | mediumint(8) unsigned | NO | PRI | NULL | |
| type | varchar(25) | NO | PRI | NULL | |
| area | varchar(255) | NO | MUL | NULL | |
+---------+-----------------------+------+-----+---------+-------+
The strange thing is that the execution time seems to be inversely related to the total number of rows returned. For example, a query like contact.area = 'United States' which returns a few thousand rows executes in less than 0.01 second. However, queries with fewer result rows such as contact.area = 'Egypt' which returns 20 rows takes in excess of 5 seconds to complete. Does my query need to be rewritten or is there a problem with the indexes?