Don’t take your vitamins
It is possible to have too much of a good thing
Fat-soluble vitamins like A, D and E are stored in the liver and adipose (fat) tissues, meaning the body can draw on supplies as and when it needs them. So we might get our vitamin E from plant oils, seeds or nuts, but we don’t need to eat them every day to make sure we have enough.
Vitamin A is important for the development of a growing fetus, including the eyes, skin, bones and immune system. However, very high levels of vitamin A are thought to cause birth defects. Thus, although much of the evidence for these adverse effects comes from animal studies, pregnant women are advised not to eat liver or pâté, and not to take fish oil supplements, because they contain too much vitamin A.
Around 70 per cent of the body’s vitamin A is stored in the form of retinyl ester molecules in large lipid droplets in the hepatic stellate cells of the liver. While adipose tissue contains less-concentrated stores, there is a lot of this tissue, so it may account for most of the remaining vitamin A.
In both liver and adipose tissue, specialised proteins called retinol-binding proteins help to put the vitamin into circulation so that it can be used elsewhere. Recent research, however, suggests that levels of retinolbinding proteins are raised in obese mice and humans, and that they may take part in signalling pathways contributing to type 2 diabetes.Lead image:
Chris Salt/Flickr CC BY NC
- List of fat-soluble vitamins and nutrients [PDF]
- Retinol and retinyl esters: biochemistry and physiology (2013)
- Vitamin A in pregnancy: requirements and safety limits (2000)
- ‘The Retinoids: Biology, biochemistry and disease’ (2015)
- Serum retinol binding protein 4 contributes to insulin resistance in obesity and type 2 diabetes (2005)
- Don’t take your vitamins PDF [PDF 71KB]