Couples who earn less than Â£42,300 less likely to be depressed
Marriage reduces the risk of depression for couples who earn less than £42,300 a year, according to new research.
But it can raise the likelihood of developing the condition among the more well off, say scientists.
The effect of wedlock on mental wellbeing has been debated for years.
Previous studies have shown married people are generally happier and healthier.
But marriage can also be one of the most significant sources of long-lasting social stress.
Now in one of the first studies of its kind sociologists have identified a link between the benefits of getting spliced and salary.
It was based on 3,617 adults in the US aged 24 to 89 who were interviewed at specific intervals over many years.
Can't buy you love?
Married individuals whose total household income was under $60,000 (£42,300) per year had fewer symptoms of depression than single people on comparable wages.
But for those above this threshold the reverse was the case.
They were more prone to the blues than high earning peers who had never been hitched.
First author Dr Ben Kail, of Georgia State University, suspects the pooling of resources helps the financially strapped feel better about themselves.
Wealthier people don't need this buffer - so having a partner bringing in money does not boost their state of mind.
Dr Kail said: "We looked at the inter-relationships between marriage, income and depression and what we found is the benefit of marriage on depression is really for people with average or lower levels of income.
"Specifically, people who are married and earning less than $60,000 a year in total household income experience fewer symptoms of depression.
"But above that, marriage is not associated with the same kind of reduction in symptoms of depression."
Happy ever after
His team examined data from the Americans' Changing Lives Survey.
The national study covers a range of sociological, psychological, mental and physical health issues and includes responses from never married, married and newly married adults.
It is among only a few to investigate whether psychological well-being in marriage varies by socioeconomic status.
Dr Kail said: "Little research has examined whether the association of marriage with psychological well-being varies by socio-economic status."
The results published in the journal Social Science Research support a theory called the marital resource model.
This suggests the health benefits of marriage include the pooling of resources - such as finances and social support.
Explained Dr Kail: "For people who are earning above $60,000 they don't get this bump because they already have enough resources.
"About 50 per cent of the benefit these households earning less than $60,000 per year get from marriage is an increased sense of financial security and self-efficacy - which is probably from the pooling of resources.
"Also, it's interesting to note, at the highest levels of income, the never married fare better in terms of depression than the married.
"They have fewer symptoms of depression than married people."
He pointed out: "All of these are sub-clinical levels of depression - meaning the disease is not severe enough to be clinically referred to as depression but can nevertheless impact your health and happiness."
In 2014 a study by another team of US scientists showed marriage can cause depression - after years of advice from experts that it makes us happier, healthier and longer-lived.
Being nagged or criticised or feeling let down by your other half were just some of the triggers for dissatisfaction with marriage found by the psychologists.
Those who suffered long-term stress within a relationship were less likely to enjoy the positive aspects of being married – a hallmark of depression.
It looked at couples after 11 years of marriage and measured how often they frowned.