The effect of vegetarian diets on iron status in adults: A systematic review and meta-analysis
Lisa M. Haider Critical Reviews in Food Science and Nutrition 2016
Background
Vegetarian diets exclude meat, seafood, and products containing these foods. Although the vegetarian lifestyle could lead to a better health status in adults, it may also bear risks for certain nutritional deficiencies. Cross-sectional studies and narrative reviews have shown that the iron status of vegetarians is compromised by the absence of highly bioavailable haem-iron in meatless diets and the inhibiting effect of certain components present in plant foods on non-haem iron bioavailability.
Methods
The databases Pubmed, Scopus, Embase, and Cochrane Central Register of Controlled Trials were searched for studies comparing serum ferritin, as the major laboratory parameter for iron status of adult vegetarians with non-vegetarian control groups. A qualitative review was conducted as well as an inverse-variance random-effects meta-analysis to pool available data. In addition the effect of vegetarian diets according to gender was investigated with a subgroup analysis. The results were validated using a sensitivity analysis.
Results
A total of 27 cross-sectional studies and 3 interventional studies were selected for the systematic review. The meta-analysis which combined data of 24 cross-sectional studies showed that adult vegetarians have significantly lower serum ferritin levels than their non-vegetarian controls (−29.71 µg/l, 95% CI [−39.69, −19.73], p<0.01). Inclusion of semi-vegetarian diets did not change the results considerably (−23.27 µg/l, 95% CI [−29.77, −16.76], p<0.01). The effects were more pronounced in men (−61.88 µg/l, 95% CI [−85.59, −38.17], p<0.01) than in both premenopausal women (−17.70 μg/l, 95% CI [−29.80, −5.60], p<0.01) and all women (−13.50 μg/l, 95% CI [−22.96, −4.04], p<0.01), respectively.
Conclusions
In conclusion our results showed that vegetarians are more likely to have lower iron stores compared with non-vegetarians. However, since high iron stores are also a risk factor for certain non-communicable diseases, such as type II diabetes, it is recommended that not only vegetarians but also non-vegetarians should regularly control their iron status and improve their diet regarding the content and bioavailability of iron by consuming more plants and less meat.
