Neuroticism is the tendency to experience negative emotion. Such people get upset and irritated easily, have mood swings and worry frequently, reports the journal Social Psychological and Personality Science.
People who score high in neuroticism are less satisfied in romance and relationships, and when they get married, they are more likely to divorce.
High levels of neuroticism are more strongly associated with bad marital outcomes than any other personality factor, said Michelle Russell and James McNulty of the University of Tennessee, study co-authors.
But sex in marriage seems to make people happy. Other research has shown that sexual interactions improved the couple's mood the next day, according to a Tennessee statement.
Russell and McNulty wanted to know if frequent sexual activity would erase the negative effects of neuroticism.
They followed 72 newlywed couples over the first four years of their marriage. Both spouses reported - separately and privately - on their marital satisfaction and sexual frequency every six months.
On average, couples reported sexual intercourse about once a week during the first six months of marriage and about three times a month by the fourth year of marriage.
Couples were considered satisfied when they said that they "have a good marriage" and "my relationship with my partner makes me happy".
Marital satisfaction was not associated with sexual frequency - neither at the start of the marriage, nor four years later.
But Russell and McNulty found one important exception. For spouses with high levels of neuroticism, frequent sexual intercourse improved their marital satisfaction.
The effect of frequent sexual activity was enough to completely wipe away the "happiness deficit" that neurotic spouses usually have.