- Higher intake of refined sugar and dairy products predict worse
2-year outcome of schizophrenia
- High national rates of depression predicted by low intake of
fish and seafood
A new study has found that a higher national dietary intake of
refined sugar and dairy products predicted a worse two-year outcome
of schizophrenia. A high national prevalence of depression was
predicted by a low dietary intake of fish and seafood.
It is known that dietary variations predict the prevalence of
physical illnesses, such as diabetes and heart disease. However,
the possible influence of diet on mental health has so far been
neglected.
Published in the May issue of the British Journal of
Psychiatry, this study was an ecological analysis of international
variations in food supply in relation to epidemiological data on
the outcome of schizophrenia and on the prevalence of
depression.
The countries included in the analysis were Denmark, Columbia,
India, Nigeria, UK, USSR, USA and Czechoslovakia for the
International Pilot Study of Schizophrenia (IPSS; World Health
Organisation, 1979); Denmark, India, Colombia, Ireland, USA,
Nigeria, USSR, Japan, UK and Czechoslovakia for the Determinants of
Outcome of Severe Mental Disorders study (DOSMED, 1992); and New
Zealand, Canada, Germany, France, USA, USSR, Taiwan and Japan for
the depression study (Weissman at al, 1996; Hibbeln, 1998).
Data on food usage were taken from the Food and Agriculture
Organisation (FAOSTAT) database (FAO, 2002). Food groups included
were meat; fish and seafood; eggs; dairy products; vegetable oil,
vegetables; cereals; fruits; starchy roots; refined sugar; pulses;
nuts; coffee; and alcoholic beverages.
The most consistent finding was that a greater consumption of
refined sugar was associated with a worse outcome of schizophrenia
and a greater prevalence of depression. Other correlations for
outcome of schizophrenia include consumption of meat and eggs
(adverse relationship) and consumption of pulses (beneficial
relationship). Dairy products and alcohol consumption were
associated with a poor outcome in the IPSS study, but not in the
DOSMED database.
For depression, the strongest association was between a high
intake of dietary fish and seafood and reduced prevalence of
depression. A high intake of dairy products and sugar was
associated with an increased prevalence of depression, whereas a
high intake of starchy roots was linked to a lower
prevalence.
Its author, Malcolm Peet, comments that these findings allow
the hypothesis that nutrition is important in the genesis and
maintenance of mental ill-health.
It is of note that diabetes, coronary heart disease and other
related conditions that cluster together have been described as
‘metabolic syndrome’ diseases. Because these disorders also cluster
with schizophrenia and depression, it has been proposed that they
may share some causal factors with physical diseases that
constitute the metabolic syndrome.
The dietary predictors of outcome of schizophrenia and
prevalence of depression in this study reflect dietary patterns
that influence insulin resistance, in particular, consumption of
large quantities of sugar and saturated fats, and lead to metabolic
syndrome diseases.
It may therefore be that altering diet could have a positive
effect on mental as well as physical health.
There is anecdotal evidence that diets that do not lead to
insulin resistance may be useful in the treatment of schizophrenia
(Meiers, 1973). Omega-3 fatty acids, found in fish and seafood,
have recently been shown to have strong positive antidepressant
benefits (Nemets et al, 2002; Peet and Horrobin, 2002).
Whether the relationship between nutritional factors and
mental health is causal can only be determined by intervention
studies
For further information, please contact Liz Fox or Deborah
Hart in the Communications Department.
Telephone: 020 7235 2351 Extensions. 6298 or 6127