A cheap way to longer life and better mental health

Multivitamins. It seems to be that simple.

Orthomolecular psychiatry is the academic term for the research into
food and mood. There's some evidence that some things work, for example
Vitamin-B and magnesium for depression in pre-menopausal women.

There's ample evidence that vitamins and minerals can increase life
expectancy too. The life expectancy of people with severe mental
illnesses is 20 years lower than the average. Many factors are cited,
for example smoking, but I think poverty and diet are significant
factors as well as the other lifestyle factors and the medication, of
course, contributes to mortality and morbidity - significantly so for
people with dementia where antipsychotics have been shown to reduce life
expectancy by 50% in one observational study in the UK.
#
A good, balanced diet with lots of fresh fruit, veg, fish, meat and all
the rest is a much better option than popping a pill, not least because
the organically bonded vitamins are absorbed better by the body.
Cheylated vitamins and minerals offer similar levels of absorption to
those from natural sources by bonding the vitamin to an amino acid.

A balanced diet is expensive. This is the problem for most people with
severe mental illnesses: they're poor. Poverty is associated with
illness and death in countless studies. Again, the factors are
important. One is being forced to buy the cheapest food, food devoid of
nutrition and high in chemicals. Not everyone cooks their meals from
scratch. Many have moved to pre-prepared meals. The cheapest version
will have less of those essential nutrients found in fresh food than the
premium meals which people who aren't poor can afford.

A high quality multi-vitamin can fill in the gaps in a person's
nutrition. Of course there's the risk of excess vitamins and minerals
which can also cause illness. Someone who drinks 5-10 pints of Guinness
every day may not need more iron for example.