Natural vs Supplementation

A multivitamin is a good idea for everybody, vegans and non-vegans alike. There's nothing wrong with supplementing as a safety net. It's cheap, and you pretty much pee out everything you don't need. In natural health food circles, which frequently have crossover within the vegan community, there is sometimes an anti-scientific fear of supplements, which can be detrimental to the movement.

Comparative ease of use

If you look at our closest primate relatives, they all eat a huge amounts of greens. That's pretty much the only way to be totally foolproof without having to put in a lot of planning. But why not just take a multivitamin, and depending on your overall diet, maybe a few other easy supplements? Supplements aren't harmful to animals or the environment, and if you go with reputable companies, not harmful to your health either. They won't give you super powers, but they're a good safety net. There are even chewable ones. And literal food with supplementation in it (ie cereals, plant milks). There's nothing wrong with taking a few supplements for convenience. It's not convenient to eat a lot of greens. It's healthy, sure, but most people don't want to eat that many vegetables.

Concerns about supplementation

High dose vitamins are not usually necessary (risk without benefit), and there's no reason to exceed the recommended daily intake (RDI) for most vitamins. There are a number of speculative mechanisms by which excess vitamins can cause problems, from inhibiting absorption to feeding cancer (which needs a large pool of nutrients to grow), even to rare direct toxicity in very high amounts which can occur with fat soluble vitamins through bioaccumulation. If you are worried about getting too much of a certain vitamin, it is necessary to understand the difference between acute toxicity, which everything has (you can kill yourself on certain whole foods too if you eat only them in large amounts), and cumulative harm. Things like carcinogens and heavy metals like mercury build up harm over time by cumulative DNA damage, or building up in your tissues. Supplements do not: your body clears out what you do not need. These are biological compounds that your body is accustomed to working with, not poisons. It's only harmful if you get a huge dose all at once. We should not confuse the fact that something can be harmful in overdose with the idea that it must be harmful in smaller doses too. We have been taking supplements for decades, and there's no good evidence of harm from them. Likewise we've been using fortified foods for a very long time, and there's so much evidence in favor for public health that it's even been legislated in many areas. Beyond that there's also TPN, Infant formula (very well studied), and the fact that we've been using supplementation with pets and farmed animals for many generations. These are well studied across species. Supplements work, and there's no credible evidence that they're harmful unless they're egregiously misused. There's absolutely no reason to believe long term consumption of modest supplements is harmful at all. We've been doing it for a very long time on population-size scales. A benefit, although small, is actually what studies have suggested.

Supplements and medicine

Supplements aren't quite in the same class as pharmaceutical drugs. They're studied like drugs, but their purpose is nutritive. Even if you want to avoid taking drugs except in serious cases, you can still have a sensible attitude toward supplements as a safety net and a way to be more casual about your diet and not worry too much. There are even synthetic forms that are actually better absorbed than natural forms. A diet containing man-made products can be healthier than a “natural" diet. And if you really want something “natural" for whatever reason, you can get bioidentical or concentrated plant derived supplements. We can track mineral supplements and follow them very easily by way of isotopes. It's a bit trickier but we can do that with synthetic vitamins too. Figuring out how something is absorbed and metabolized is a very active field of medicine. We don't even need to do that all the time, though, when we can take somebody with deficiency, give the person a supplement, then observe the deficiency to be corrected.

Supplements compared to limited animal consumption

If you're only eating a vegan diet for health reasons, there's still reason to believe taking B-12 and iron is healthier than eating a bunch of beef, taking calcium is healthier than drinking a bunch of milk, and taking Omega 3s is healthier than eating a bunch of fish. With plants and supplements you're getting the good without the bad. Harm from supplements vs. animal products are quite different. Again, one (supplements) has only to do with having too much of something and is not innate to the substance, the other (animal products) seems to carry some innately harmful substances. Having animal products less often, like smoking only occasionally, will surely lessen the harm, but there's no reason to believe that's better than just getting those nutrients from supplements. The only argument health-care professionals can make for fish as better than Omega DHA/EPA supplements is that it acts to *displace* other less healthy food from the diet (e.g. fish instead of beef), not that it's inherently better. And in fact, there are good reasons to believe a serving of tofu + a DHA/EPA supplement is going to be better than fish in the long run. Somebody on a standard american diet is, in terms of health, better off eating fish than taking DHA/EPA, but that's because the consumption of fish will displace beef or other worse foods, not because the fish is better than tofu. That's the logic of essentially all public health advice. Is it healthier to get all of your nutrients from vegetables? Probably, but that's because vegetables have other things in them (phytonutrients) that benefit health. There's no reason to think it's healthier to get those nutrients from animal products which lack those health boosting substances and instead tend to have contamination and health harming substances -- much worse contamination than supplements. There's nothing indicating that eating animal products and NOT taking supplements has a better outcome (that's something we do have data on and would be apparent). That's the point of listening to the registered dietitians when it comes to advice on supplements. None of them are recommending large doses or fad supplements. But they, and governmental bodies, support modest supplements, either as vitamins we take or that are added to fortified foods (even by law, because the science is so overwhelming)

“Natural” vegan compared to “supplement” vegan

Taking large amounts of a particular supplement can be a problem, because even if your body down-regulates absorption it can interfere with another vitamin or mineral with a similar pathway. But the benefits of modest supplementation is mainstream vegan consensus. Many foods (and even tap water in some places) have been fortified for decades for everybody because of the overwhelming evidence for supplementation to improve public health. Look at refined grains (they're not great because they're lacking fiber, but fortifying them helped a lot). Maybe there's some state of ideal human nutrition that gives you superpowers that comes from eating 100% plants and getting all of your nutrients that way, but there's no evidence for it. Humans have requirements for certain nutrients, not certain sources of nutrients. It doesn't matter what form those nutrients are in or where they came from as long as they resolve the deficiency. Also, supplements do not stop working just because you take them indefinitely. In many cases they are and remain better than "natural" food sources. It's very plausible that getting enough nutrients from vegetables has an even better outcome, but we don't really have much data on that because very few people actually do that.

Epidemiological evidence

The epidemiological evidence for supplements is clear. Fortify food with supplements and your population has better health outcomes. In terms of pills, we have literally decades long studies like the nurses' health study that don't show any harm from modest supplements, and to the contrary often correlate to better health. It's reasonable to be skeptical of those correlations because people more likely to supplement may also be likely to have other healthier lifestyle factors that aren't well enough controlled for, but it's not credible to assume supplementation is harmful. To the contrary, the lack of evidence of harm in those studies is strong evidence that they're not harmful or if so they do so little harm that it's undetectable. The only harmful effects ever demonstrated have been from very high doses. The supplements we're talking about are quite well studied. We know they're fine to a degree of certainty it is unreasonable to doubt. And by far to a degree of certainty that it's not justified to harm animals and the environment.

Appeal to evolution argument

An appeal to evolution is a terrible argument for optimal nutrition since on our "natural" diets our ancestors didn't live anywhere nearly as long as we do today. There are any number of problems a "natural" diet can cause in old age that we wouldn't have evolved resistance against. If something didn't kill us before reproduction in our 20s to 30s, then we wouldn't have adapted to it. We only have strong evolutionary pressure for resistance to things that kill us before reproduction.

Public Health

Some study authors and public health personalities are concerned with people being stupid and taking too much of certain vitamins. This is why it may be poor public health advice to just recommend people take vitamins instead of eating vegetables, which is why that isn't done. Veggies contain a lot of beneficial substances that can not typically be obtained from a multivitamin, and more importantly they fill people up and push out unhealthy foods. However, vegans already eat considerable amounts of veggies, and at a certain point there are diminishing returns from the fiber and phytonutrient intake. There's no reason not to recommend modest supplements to make it easier to stick to, which is why dietitians readily recommend modest supplementation and fortified foods for vegans since they're not that worried about us not eating our veggies. Would eating more vegetables instead of taking a vitamin be healthier? Probably, but we're talking about theoretical optimal nutrition here, not adequate nutrition. We're not talking about a difference in suffering ill health or anything even noticeable, but a fraction of a percentage reduction in the chance of getting certain cancers etc. The only reason to think recommending vitamins could be "bad" is the same reason recommending fish is "good". Fish displaces worse things in the diet like meat. If people think they can take vitamins and eat junk food all day, likewise, that could be a problem. If vitamins displace healthy food that's an issue, but if you're eating a lot of veggies already and if they're just making it easier not to eat animal products there's no reason to think that's a problem. Vitamins are only an issue if you use them as a license to eat junk food all day instead of healthy food.

Risk

The "risk" of taking supplements is not only small, but a "negative risk" because the chance of benefit is higher than the chance of harm. A reduction in mortality for modest supplements like multivitamins is based on epidemiological (real world) data. It’s possible that an air bag fear phenomena is analogous here. People take vitamins to reduce their risks (and by all existing data, they do reduce risk a little) but because of this they're inordinately afraid of being harmed by vitamins. Studies have also indicated that most people have sub-optimal levels of some nutrients. Obviously if you have adequate status in everything, supplements aren't going to be useful. That's why high dose supplements aren't any good. Even badly sourced supplements with higher amounts of heavy metals are going to contain less than fish, for example. But the nice thing about supplements is that you can choose more reputable companies, and you can even mix it up to hedge your bets in case one is a little lower in something than labeled.