- Vitamin metabolism is complex
- Vitamin A: plant and animal sources
- Vitamin A deficiency in Vegans
- BCO1 Genes and Vitamin A
- Vitamin A and retinol supplements warning
- Modifications to a vegan diet to get Vitamin A
- Key Takeaways
Vitamin metabolism is complexOne of the fascinating things about nutrigenomic research is the opportunity it affords to study the metabolic efficiencies of the human body. Many of our “nutritional inputs” have to change form before they’re useful as fuel for our cells, and our genes play an important role in helping to produce the enzymes that break down nutrients into a form the body can use. For example, it’s the VDR genes that help us make the active form of vitamin D, called calcitrol, so it can be used to absorb calcium from the gut. Similarly, our MTHFR genes help us break down folate into 5-MTHF (methyl folate). The short chain omega-3 fats, like alpha linoleic acid, must be converted to the long chain EPA and DHA, and some of us with certain FADS1 variants, don’t convert any ALA into DHA, which could contribute to a decline in mental health for some people.1 This article discusses our BCO1 genes, and how they influence the body’s ability to convert beta-carotene into an active form of Vitamin A, called retinol.
Vitamin A: plant and animal sourcesVitamin A is a powerful antioxidant responsible for supporting healthy skin, vision, bone growth, and immune function, among other things. We can get Vitamin A from both plant and animal sources. 2
RetinolEggs, for example, are rich in a form of Vitamin A called retinol. Retinol, famous in many circles as the main ingredient in anti-aging skin treatments, is readily bioavailable, meaning it is consumed in a form the body can make use of right away.
CarotenoidsThe other source of Vitamin A comes from fat soluble antioxidants known as carotenoids, which are plant based. Beta carotene, found in foods like carrots and yams, is a type of carotenoid that our bodies convert to Vitamin A (retinol). 3 We are easily able to absorb retinol derived from animal products, however, the bioavailability of plant based sources is more limited, meaning we lose Vitamin A in the process of converting beta-carotene to retinol. 4
Vitamin A deficiency in VegansThis is where the possibility for a vitamin A deficiency comes into play, especially for vegans. Since our bodies aren’t as effective at breaking down plants into vitamin A, a diet that excludes all animal based products could set the table for a Vitamin A deficiency. This possibility increases when certain variants or “mutations” in our BCO1 genes are present.
BCO1 Genes and Vitamin AThere is genetic variability in B-carotene metabolism. Some process beta-carotene into Vitamin A more efficiently than others. 5 The protein encoded by the BCO1 gene, called beta-carotene 15,15′-monoxygenase (BCMO1), is a key enzyme in beta-carotene metabolism to vitamin A. 6 Two common SNPs of the BCO1 gene, (R267S and A379V) have shown a decreased ability to metabolize beta carotene into retinol. 7 Just as certain SOD2 A16V alleles result in lower amounts of superoxide dismutase, certain BCO1 variations result in lower amounts of BCMO1, and therefore reduced amounts of bioavailable Vitamin A for carriers. The “risk” allele for BCO1 R267S is T. The “risk” allele for BCO1 A379V is also T. Note: to date, the studies showing a decreased ability to convert beta-carotene to Vitamin A for these SNPs have only been performed in women, the evidence is inconclusive as to men. 7 For those with genotypes associated with a reduced ability to gain vitamin A from plant sources, a vegan diet could present some nutritional challenges, because some studies show that vitamin A supplementation isn’t a great solution either.
Vitamin A and retinol supplements warningWe’ve established there are genetic variants of the BCO1 gene that put women (and possibly some men) at a disadvantage in accessing Vitamin A from plants. Perhaps this is why some Vegans turn orange on a high beta-carotene diet? They’re simply not converting beta-carotene to retinol effectively, and it starts to pool in their bodies. Does this mean Vitamin A supplements, or even animal sources of Vitamin A are advisable? Let’s discuss each in turn.
Beta-carotene in food is healthyFor starters, studies show diets (we’re talking food here) high in carotenoids are healthy, and may reduce the risk of certain diseases. This study discusses the protective effect dietary beta-carotene can have on developing many types of cancers. This study analyzed dietary beta-carotene’s protective impact on heart disease. This study discusses how dietary Vitamin A can protect against macular degeneration.
Why you might want to avoid Vitamin A supplementsHowever, there is evidence suggesting that food should be the preferred delivery mechanism for Vitamin A, as the same benefits are not conferred from supplements alone. 8 9 This study saw an increased risk for lung cancer and heart disease of 20% when beta carotene consumption exceeded the recommended dosage. This study found a significant increase in hip fracture risk in postmenopausal women taking Vitamin A supplements and retinol in fortified food. To quote the study:
Long-term intake of a diet high in retinol may promote the development of osteoporotic hip fractures in women. The amounts of retinol in fortified foods and vitamin supplements may need to be reassessed.It’s also important to note that dietary beta-carotene, as opposed to Vitamin A supplements, did not increase the risk for fracture.