"Eating fish during pregnancy can help reduce feelings of anxiety ahead of giving birth,” advises The Daily Telegraph. The story is based on research which asked more than 9,500 pregnant women about their diets…
”Eating fish during pregnancy can help reduce feelings of anxiety ahead of giving birth,” advises The Daily Telegraph.
The story is based on research which asked more than 9,500 pregnant women about their diets and their levels of anxiety.
Women who ate oily fish one to three times a week were less likely to report high levels of anxiety than those who never ate it.
Some other findings of the study were largely ignored by the media. For example, women whose diets conformed to more health conscious patterns (for example, those high in foods such as fruit, salad, oat and bran cereals, and fish) or traditional patterns (vegetables, red meat, poultry) were less likely to report high levels of anxiety symptoms than those whose diets didn’t.
The main limitation to these findings is that diet and anxiety symptoms were assessed at the same time, so it is impossible to determine whether there was a direct cause and effect relationship between diet and mood.
It could be that feeling anxious may affect food choices for some women, or that other factors affect both women’s anxiety levels and diet.
Also, although the researchers took into account many factors that could be influencing anxiety, others, such as physical activity, could still be having an effect.
Although this study cannot prove by itself that diet directly affects anxiety levels in pregnancy, following a healthy balanced diet is known to be important for both the mother and baby in pregnancy. Read more about healthy eating in pregnancy
Oily fish in pregnancy
Current UK recommendations are that pregnant women try to eat two portions of fish a week, one of which should be oily fish such as salmon, sardines or mackerel. Women are advised not to eat more than two portions of oily fish a week.
Pregnant women should not eat shark, marlin and swordfish as these contain high levels of mercury that could damage the baby’s development. Pregnant women should limit their consumption of tuna to no more than 140g cooked tuna per week for the same reason.
Where did the story come from?
The study was carried out by researchers from the Federal University of Pelotas in Brazil and other research centres in the UK and US. The study was funded by the UK Medical Research Council, the Wellcome Trust, the University of Bristol, UK Department of the Environment and the Ministry of Agriculture, Fisheries, and Food, US National Institute on Alcohol Abuse and Alcoholism, US National Institutes of Health, and John M. Davis.
The study was published in the peer-reviewed, open access journal: PLoS One.
The Daily Telegraph covers this study in a reasonable way and responsibly includes a mention of NHS guidelines on eating oily fish in pregnancy. However, the inherent limitations of the study design employed by the researchers could have been made more explicit.
What kind of research was this?
This was an analysis of cross sectional data from an ongoing cohort study called the Avon Longitudinal Study of Parents and Children (ALSPAC) study. The study aimed to look at whether there was an association between dietary patterns, seafood consumption and the type of fats in oily fish (n3 PUFAs – commonly known as omega3 fatty acids) and levels of anxiety in pregnant women. The researchers thought that less health conscious diets, including lower consumptions of seafood and n3 PUFAs, might be associated with higher levels of anxiety.
Although the ALSPAC cohort is following pregnant women and their offspring over time, the current study was based on questionnaires completed at one point in time. Therefore, as such, researchers cannot determine whether the women’s dietary patterns were established before their current levels of anxiety.
What did the research involve?
The researchers gave the 9,530 women taking part a questionnaire about their diets and levels of anxiety at 32 weeks into their pregnancy. They then looked at the relationship between the two.
Women with multiple pregnancies (such as twins) were not included in the current study. The eight questions on anxiety had been tested and shown to be a reliable measurement tool for anxiety symptoms.
They asked the women how often they experienced various signs of anxiety, such as how often they felt “upset for no obvious reason” or felt that they were “going to pieces”. Women who scored in the top 15% were considered to have high levels of anxiety symptoms.
The food questionnaire included 110 questions about how often they ate from 43 different food groups and food items, and eight basic foods. The questionnaire did not assess how much of the foods they ate. The researchers used the women’s replies to classify their dietary patterns according to five previously defined groupings:
health-conscious: salad, fruit, fruit juice, rice, pasta, oat/bran based breakfast cereal, fish, pulses, cheese, non-white bread
- traditional: vegetables, red meat, poultry
processed: meat pies, sausages, burgers, fried foods, pizza, chips, white bread, eggs, baked beans
confectionery: chocolate, sweets, biscuits, cakes, puddings
vegetarian: meat substitutes, pulses, nuts, herbal tea and less red meat and poultry
The women were also asked about how many times a week they currently ate:
- white fish (cod, haddock, plaice, fish fingers, etc.)
- dark or oily fish (tuna, sardines, pilchards, mackerel, herring, kippers, trout, salmon, etc.)
- shellfish (prawns, crabs, cockles, mussels, etc.)
Answers could be; never or rarely, once in two weeks, one to three times per week, four to seven times per week, or more than once a day. The researchers used this data to calculate how much n-3 PUFA the women consumed.
In their analyses, the researchers took a range of factors into account (potential confounders), including:
- highest educational qualification achieved
- work status (employed, unemployed)
- housing status (mortgaged/owned, council rented – public housing, other)
- house crowding
- maternal smoking during first trimester of pregnancy
- maternal alcohol consumption during first trimester of pregnancy
- number of previous pregnancies resulting in a live birth or a late fetal death
- previous history of abortion
- previous history of miscarriage
- stressful life events in childhood
- stressful recent life events
- chronic stress as measured by a family adversity index
What were the basic results?
Women with high levels of anxiety symptoms were more likely to be:
- younger (<25 years)
- have lower education levels
- be unemployed
- be living in council-owned (public) housing and in households with more overcrowding
- have two or more children
- have a previous history of abortion and miscarriage
- experienced high levels of adverse life events in childhood as well as recently
- high levels of chronic stress due to family adversity
After taking into account these potential confounders, the study found that:
- women with the most “health-conscious” diets were 23% less likely to report high levels of anxiety symptoms than women with the least “health-conscious” diets (odds ratio [OR] 0.77, 95% confidence interval [CI] 0.65 to 0.93)
- women with the most “traditional” diets were 16% less likely to report high levels of anxiety symptoms than women with the least “traditional” diets (OR 0.84, 95% CI 0.73 to 0.97)
- women who had no n-3 PUFA intake from seafood were 53% more likely to report high levels of anxiety compared with those with intake of over 1.5 grams/week. (OR 1.53, 95% CI 1.25 to 1.87)
- women who had eaten no dark or oily fish were 38% more likely to report high levels of anxiety compared with those who ate it one to three times a week or more (OR 1.38, 95% CI 1.19 to 1.62)
- one surprising result is that women with the most “vegetarian” pattern of diet were 25% more likely to report high levels of anxiety compared with those with the least “vegetarian” pattern of diet (OR 1.25, 95% CI 1.08 to 1.44)
How did the researchers interpret the results?
The researchers concluded that their findings show a relationship between dietary patterns and n-3 PUFA intake from seafood and symptoms of anxiety in pregnancy. They suggest this means that “dietary interventions could be used to reduce high anxiety symptoms during pregnancy”. They do note that clinical trials would be needed to test whether this would be the case.
The current study suggests an association between specific dietary patterns (“health conscious” and “traditional” patterns) and n-3 PUFA intake from seafood and anxiety in pregnancy. Its strengths include its large size and ability to assess and take into account a large number of factors.
There are two main limitations to these findings. Firstly, diet and anxiety symptoms were assessed at the same time, therefore the researchers cannot tell whether the dietary patterns were established before the women started to experience anxiety or not. Secondly, the association may be being influenced by factors other than diet.
The researchers took a wide range of factors into account in their analyses, such as the women’s experience of stressful life events, and indicators of their socioeconomic status. However, mental health, and how it can be influenced, is an extremely complex issue so there may well be other factors which could be having an effect. For example, physical activity was not assessed and could have an impact.
Overall, this study by itself cannot prove that your diet directly influences anxiety in pregnancy. However, the “health conscious” and “traditional” patterns of eating and diets including oily fish that were associated with lower anxiety in this study seem likely to be what would be considered a healthy balanced diet. And following a healthy diet is already known be important for the health of both mother and baby.
Read more about healthy eating during pregnancy as well as what foods to avoid.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter.