In general, I’m against the genetic modification of food crops. Corporations modify crops mainly for the benefit of the corporation, especially to make a larger profit. However, there are some legitimate uses for GMO (genetically modified organisms). A plant might be modified to produce a biotech medicine. A plant might be modified to protect against a plant disease that would otherwise devastate a world staple crop, upon which depends the lives of many persons. And, in the case of this proposal, a plant might be modified to provide a nutrient that is otherwise unavailable to persons who do not consume animal source foods.
Vegans decline to eat foods from animals: beef, pork, poultry, fish, milk, cheese, eggs, and even products like honey, which are produced by animals (bees). Honey is to bees as milk is to cows, and as eggs are to chickens. To obtain the necessary vitamin B12, vegans must take a vitamin supplement. Most claims that B12 is available in plant-based foods are not supported by science. It is possible to obtain some B12 from plants grown in fresh manure, but the amount of B12 is too small, and the availability of such plant foods is highly limited.
Why not just take a supplement?
Supplements are not available to everyone in the world. The undernourished in the developing world do not have access to supplements, even if they had the money needed to buy them. Many persons still depend upon food they grow themselves for their nutrition.
How does this help non-vegans?
Animal source foods require more land and other agriculture resources than most plant source foods. As the world population increases, and agricultural land is converted to other uses, it become ever more important to obtain more food from less land. Animal source foods will necessarily decrease in availability and increase in cost, making it important even for non-vegans to have a plant-based source of all vitamins, especially B12.
Which food should be modified?
We can’t modify a staple crop, nor any food that is eaten in large quantities, as some persons would obtain too much B12 as a result. There is no tolerable upper limit to vitamin B12, according to the Institute of Medicine’s food and nutrition board. PDF file But due caution is required. Too much of any vitamin or mineral might cause health problems.
On the other hand, it must be a food that is eaten by many persons. It must be compatible with a wide range of different cuisines in cultures throughout the world. And yet be a food that is self-limiting in quantities. Suppose that food is your favorite food above all else. It should still be something not eaten in quantities that would provide an excess of the vitamin.
Then, at the other end of the range, it should be a food that can be eaten in modest amounts, and still provide 100% of the recommended amount of B12.
For children as young as 9 years old to elderly adults, including women who are pregnant or lactating, the range of recommended intake for vitamin B12 is from 1.8 to 2.8 micrograms (mcg). The value for B12 is micrograms, while the value for vitamin B6 is milligrams. The human body requires about 714 times as much B6 as B12 (2.0 mg vs. 2.8 mcg).
Instead of using the “daily value” for these vitamins, I’ll be using the highest value, which turns out to be 2.0 mg for B6, 600 mcg folate, and 2.8 mcg for B12. That way everyone has as more of these vitamins as the need, or more.
The GMO program will only cause the plant to make vitamin B12. vitamins B6 and folate are found naturally in many plants. Since these three are related, a plant should be chosen which produces the right proportion of B6 to folate. Excess folate (folic acid) can be harmful. So we have to make certain that, in eating enough of the food to obtain your daily amount of B12, you don’t consume an excess of folate.
The methyl-folate trap is a term referring to a biochemical problem in humans when they consume both too much folate and too little B6 and B12:
“vitamin B12 deficiency can lead to lowered levels of methionine synthetase, which results in a functional folate deficiency by trapping an increased proportion of folate as the 5-methyl derivative.” 
“Current epidemiological evidence suggests that an imbalance of high folate status and low vitamin B12 status is associated with negative health outcomes in older adults and children.” 
The technical explanation boils down to this: if you have too little B12, then no matter how much folate you have in your diet, it does you no good. In addition, the buildup of the methyl derivative of folate can be unhealthy.
So the plant food that is modified to add B12 should have the right proportion of folate, specifically less folate than B12, but enough to contribute substantially to the folate in a normal healthy diet. You don’t need to get all of your folate from the modified food, but some would be helpful in assuring that both vitamins are in the diet.
The three vitamins, B6, folate, and B12, are each and all involved in producing red blood cells. So they are interrelated in function. That is why the food that is modified to have B12 should also naturally contain B6 and folate, in the right proportions (more B6 and B12 than folate).
Which food has B6 and folate, in the right proportions, and meets the other conditions stated above? Peppers. Sweet Bell Peppers. This food has plenty of both B6 and folate, but more B6 (proportionately more) than folate. Proportionately more means that if you eat enough of the food to obtain the recommended minimum of folate, you have more than the recommended minimum of B6. And that’s what you want.
Can it be done?
I’m still looking into the feasibility of the project. But pepper plants are ideal. They are easy to grow indoors or outdoors. They do not require a lot of land. They can be pollinated by hand. Many varieties exist from which to choose.
I would suggest orange bell peppers, as they also provide zeaxanthin, betacryptoxanthin, and both beta- and alpha-carotene.  As long as we are giving persons B6, folate, and B12, we might as well give them some healthy carotenes too. Zeaxanthin, in particular, is not found in very many foods. The orange-colored bell peppers are one of the few good sources of that nutrient. Adding B12 will encourage more persons to eat the food, and will therefore benefit them via the zeaxanthin and other carotenoids.
The orange color is helpful, in that it identifies this particular type of bell pepper as the one with B12. I considered using purple bell peppers, as a more unique identifying characteristic, but the purple color is lost upon cooking. Yes, there will still be orange bell peppers that are non-GMO and have no B12. So the color is not the sole identifying characteristic.
Bell peppers grow well in hot weather, which is helpful to many of the developing regions of the world (where micronutrient deficiencies are common). The plant can be grown indoors or in greenhouses in colder climates.
How Much B12?
Here’s the RDAs for different ages:
0.9 mcg kids 1 to 3
1.2 mcg kids 4 to 8
1.8 mcg kids 9 to 13
2.4 mcg ages 14 to 140
2.6 mcg pregnant women
2.8 mcg lactating women
Suppose 10 grams of raw red peppers provides 1 mcg of B12. That weight is equal to one rounded tablespoon of chopped peppers . One and a half tablespoons or 15 grams would be sufficient for children 4 to 8 years old at 1.5 mcg. Two tablespoons or 20 grams would be 2.0 mcg which works fine for kids 9 to 13 years old. Then 30 grams or about one ounce will provide all the B12 that adults need, 3.0 mcg.
It is not a problem for water-soluble vitamins like the B-vitamins to be taken in modest excess of the RDA (which is a minimum recommended amount, not a maximum). And there’s not maximum for B12, no “tolerable upper limit”.
On the high end, a pound of raw bell peppers would be 45 mcg of B12. That’s a lot of peppers to eat. But vitamin B12 supplements are often taken in amounts as high as 500 to 1000 mcg. So even at 1.0 mcg per 10 grams of bell pepper, no one is going to overdose on B12.
Ronald L. Conte Jr.
 Shane, Barry, and EL Robert Stokstad. “Vitamin B12-folate interrelationships.” Annual review of nutrition 5.1 (1985): 115-141. PubMed
 Paul, Ligi, and Jacob Selhub. “Interaction between excess folate and low vitamin B12 status.” Molecular aspects of medicine 53 (2017): 43-47. Science Direct
 Perry, Alisa, Helen Rasmussen, and Elizabeth J. Johnson. “Xanthophyll (lutein, zeaxanthin) content in fruits, vegetables and corn and egg products.” Journal of Food Composition and Analysis 22.1 (2009): 9-15. Science Direct
 U.S. Department of Health & Human Services, National Institutes of Health, Food and Nutrition Board, Dietary Reference Intakes, Recommended Dietary Allowances and Adequate Intakes, Vitamins
 Basic Report: 11821, Peppers, sweet, red, raw