Vitamin A is a critical nutrient for healthy skin, no doubt about it. As a powerful antioxidant, Vitamin A and its related compounds (you’ve probably heard of “beta carotene/carotenoids”) scavenge the body for free radicals, damaging chemical compounds that have been associated with the development of skin cancer. Think of vitamin A and other antioxidants as cellular bounty hunters, looking for the bad guys seeking to cause damage and disease, and, you know, taking care of the problem. Diets higher in vitamin A tend to be associated with lower rates of skin cancer occurrence. So, if vitamin A is good, more of it must be great, right? As with so many things involving health, dose (amount) and form (food vs. supplement) matter. Before I hit you with the research results, let’s take a step back and gain some understanding about why it matters whether a research study looks at vitamin A obtained through food or vitamin A obtained through supplements.
As a general principle, it is quite difficult to “overdose” on any vitamin or mineral through food alone. For instance, to equal the amount of vitamin C in a typical immune-boosting/cold prevention supplement, you’d need to eat more than 20 large oranges. Just imagine the difference in volume between a refrigerator full of oranges versus the tiny packets containing vitamin C in its powdered, supplement form. Both provide identical forms of vitamin C, chemically speaking, but there is obviously a whole lot more “stuff” in 20 oranges than 2 tablespoons of powder. That “stuff” consists of everything from water, fiber, other vitamins and minerals, and trace amounts of other compounds that helped the orange tree grow and may help the vitamin work better. Now, consider the supplement packet containing pure, isolated Vitamin C, stripped down and ready to be absorbed and carry out its function.
Now that you’ve envisioned the difference, start to think about how this might impact the ways in which we conduct and understand research relating to essentially any vitamin or mineral. Clearly, there is a massive difference between vitamin C provided by 20 oranges, + all the other “stuff”, which may enhance or inhibit how this vitamin works, vs. the vitamin C provided by a purely supplemental form containing no possible blockers or enhancers. There is also a physical limit of the amount of any vitamin that can be provided by food (do you actually want to eat 20 oranges)? Keeping this in mind helps us understand how two studies, designed differently but studying the same nutrient, can report different results.
Back to the reason you started reading this post in the first place: vitamin A supplements and skin cancer. To give away the ending, despite the fact that diets high in beta carotene-containing foods are protective against skin cancer, beta carotene supplements do not appear to offer the same benefit. In 2010, The International Journal of Cancer published a meta-analysis (AKA, meticulous review of research done to date) evaluating the role of beta-carotene supplementation and cancer prevention. They looked at hundreds of studies tying vitamin A supplementation back to the risk of many types of cancers and found that not only was supplementation not protective, it actually mildly elevated the risk of skin cancer in women. The recommendation of these researchers was to employ food and lifestyle-based strategies for cancer prevention, rather than antioxidant supplements.
Hold the phone. If there is a general understanding that vitamin A is a skin-protecting antioxidant, and people who eat more vitamin A are less likely to get skin cancer, how can these results be true? To answer this, we must dig a bit deeper into the biochemistry of vitamin A and how it functions as an antioxidant. The free radical compounds mentioned earlier actually cause damage because they have what’s called an “unpaired electron,” a problem that can only be fixed by pairing up with another compound. As it turns out, the sub-cellular dating scene is just as messy as in real life, and in the process of bouncing around looking to bond, they end up causing damage to DNA and cell membranes, which can increase cancer risk. Antioxidants like vitamin A neutralize free radicals by giving up one of their own electrons, but this unselfishness means that in turn, they end up needing to pair themselves. This creates a bit of a lose-lose situation on the free radical front, as vitamin A creates the exact problem it was trying to fix. At this point, vitamin A desperately needs to pair up with another antioxidant, like vitamin C, or lycopene, because no good deed goes unpunished. Quick problem, though. When taken in isolation, vitamin A is less likely to encounter another antioxidant like vitamin C in that moment. One study describes it this way: “…the protective effect of beta-carotene...might depend on interaction with other dietary factors …those factors could be other carotenoids, their isomers, or some yet unidentified phytochemical(s).” Quantity also plays a role. If you consume megadoses of vitamin A from supplements, pair that with a poor diet and high levels of circulating free radicals, you can see how the need to re-pair the “used up” vitamin A actually creates an even larger antioxidant deficit. We don’t see this same problem when vitamin A is consumed in the form of whole foods, in part because they simply provide a more manageable amount of the nutrient. To quote a 2015 publication in the Journal of Skin Cancer review article, Diet and Skin Cancer: “when consumed in a fruit or vegetable, these antioxidants are consumed in relative quantities with one another that may be vital to their antioxidant qualities.”
Ultimately, supplements can and do play a role in health, so we shouldn’t downplay their importance. Iron supplements are essential during most pregnancies, and a large constituent of the population could improve their health and address their underlying vitamin D deficiency with a daily supplement, to name two examples. This is why each nutrient warrants its own investigation and research, and why nutrition is ultimately an individual undertaking. Focusing on whole, nutrient-dense foods is always a safe approach as we unlock more knowledge about how every part of a food, down to its individual molecules, contributes to its impact in the body. As one researcher put it: “It is well recognized that there is a complex interplay of nutrients present in naturally occurring foods. In consuming a diet based on whole foods, the finely balanced proportion of nutrients, the large number of potentially protective compounds, and the other plant constituents (such as fiber) may all be necessary. Some compounds may potentiate the effects of others, and the role of synergy may make the whole more powerful than the sum of its parts. While there has historically been a focus on the effects of isolated nutrients in human subjects, it is just as vital, if not more so, to continue to study the effects of the entire package of interacting nutrients and substances found in whole foods.”
Rajani Katta and Danielle Nicole Brown, “Diet and Skin Cancer: The Potential Role of Dietary Antioxidants in Nonmelanoma Skin Cancer Prevention,” Journal of Skin Cancer, vol. 2015, Article ID 893149, 10 pages, 2015. https://doi.org/10.1155/2015/893149.
Druesne‐Pecollo, N. , Latino‐Martel, P. , Norat, T. , Barrandon, E. , Bertrais, S. , Galan, P. and Hercberg, S. (2010), Beta‐carotene supplementation and cancer risk: a systematic review and metaanalysis of randomized controlled trials. Int. J. Cancer, 127: 172-184. doi:10.1002/ijc.25008
Disclaimer: This information is educational only and not providing healthcare recommendations. Please see a healthcare provider.