https://nutritionfacts.org/topics/vitamin-b12/
Recommended vitamin B12 doses.

https://nutritionfacts.org/video/vegetarians-and-stroke-risk-factors-vitamin-b12-homocysteine/
Vitamin B12 deficiency increases risk of stroke.

When exposed to sunlight, human skin makes its own vitamin D. But the sun also causes skin cancer.

Doctors have varying opinions on dietary vitamin D supplementation.

• Dr. Greger recommends supplementing vitamin D.
  https://nutritionfacts.org/2019/04/30/what-is-the-optimal-vitamin-d-level/ 2019
  https://nutritionfacts.org/video/take-vitamin-d-supplements-with-meals/ 2011
  Take vitamin D3 supplement with a meal.
• https://nutritionfacts.org/video/the-risks-and-benefits-of-sensible-sun-exposure/ 2016
  The threat of skin cancer is real. However, it’s mostly from chronic excessive sun exposure and sunburns. There’s little evidence that minimal, sensible exposure to sunlight will considerably increase the risk of skin cancer.
• Vitamin D Pills Are Useless, 2018 by Jeff Nelson at VegSource
  https://www.youtube.com/watch?v=bflE6ubv7tw
  [Nelson also posted updates in the comments.]
• Sun exposure has other benefits, some of them are unknown. We don't know what we don't know. So better to be conservative and get vitamin D the natural way, from the sun.
  The Cumulative Effects of Vitamin D Supplementation, 2015 by Popper
  https://www.youtube.com/watch?v=vPwZfzb8nno
  4:01 We don't know what the long-term consequences of vitamin D supplementation are.
• Vitamin D Supplements Are Harmful —Sunshine and Food Determine Health, 2005 by Dr. McDougall
  https://www.drmcdougall.com/misc/2015nl/mar/vitamind.htm

Sunlight and Vitamin D, A global perspective for health, 2013
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3897598/
The skin synthesize vitamin D from UVB. Sun induced vitamin D synthesis is greatly influenced by season, time of day, latitude, altitude, air pollution, skin pigmentation, sunscreen use, passing through glass and plastic, and aging.

Eat 1 or 2 Tbsp of flaxseed meal per day for Omega-3.

Whole flaxseeds will pass through your body undigested if you don't grind them. Grind a cup of whole flax seeds in a coffee grinder, and then store the resulting flaxseed meal in the refrigerator for up to a month.

Store whole flaxseeds away from heat and light. Omega-3 in flaxseed meal degrades when exposed to oxygen, heat, or light. Therefore, store-bought flaxseed meal likely contains lower levels of omega-3 than whole flaxseeds.

There are two kinds of Omega-3: AHA and DHA. Evidence for Omega-3 AHA supplementation is weak. Omega-3 AHA supplements thin blood which could benefit some SAD eaters. There is no evidence that Omega-3 AHA supplements benefit WFPB eaters. Evolution has likely equipped WFPB eaters to convert Omega-3 ALA to DHA as needed.

Dr Greger’s DHA Advice Is Not Sound by Jeff Nelson at VegSource, 2019 (11-minute video)
https://www.youtube.com/watch?v=rc78KfPbsa8
You don't need DHA supplements.

Do Vegans Need DHA Supplements? by Jeff Nelson at VegSource, 2019 (71-minute video)
https://www.youtube.com/watch?v=c8_kTtWUnf8
Nobody needs to take DHA supplements if you're following a healthy lifestyle.

DHA: On Further Thought…, 2020 (21-minute video)
https://www.youtube.com/watch?v=e3FuKCsWvKE
Doctor Klaper explains why he does not recommend supplemental DHA.

Vegans and people who eat few or no dairy products, seafood, and eggs might not obtain sufficient amounts of iodine. Iodine is most important to pregnant women.

Recommended Intakes and Sources of Iodine https://ods.od.nih.gov/factsheets/Iodine-HealthProfessional/#h3

Except for vitamin B12 and vitamin D, the WFPB diet provides all the nutrition humans need if you eat enough to maintain a healthy weight. Yet some WFPB eaters feel the need to supplement with superfluous foods, protein, vitamins, or minerals. Dr. Douglas Lisle uses evolutionary psychology to explain this human behavior.

Potato Strong interviews Dr. Douglas Lisle 2016 (10-minute video segment)
https://youtu.be/Gc3XfIOxTLU?t=3171

• 52:51 Potato Strong: There is some difference of opinion on [simple] starch-based diet … [vs.] the Nutritarian Dr. Fuhrman, and Dr. Greger to some extent. What is your take on some of these nutrients that people seem to think they have to have?
  Lisle: This issue of nutrient density and concern about nutrients is minor league… it is not an important issue. People around the world often lived in ecological circumstances where the diets were extremely narrow. When the body is faced with a diet that is very low in a nutrient (vitamin or mineral) the genes have mechanisms to recycle those nutrients very efficiently. For every individual that has their health compromised by some vitamin or mineral deficiency, there are a thousand people that have their health compromised because of dietary excesses. I tell people to never worry about dietary deficiency.
• 55:45 People are wired to worry about deficiency because the threat of dying from starvation was an important problem for humans, and all species. So the concept of deficiency is front and center in peoples' considerations and worries. That comes naturally to people. What does not come naturally is worrying about dietary excess. No [prehistoric] human has died of dietary excess. This was never a problem for any species. It is only a problem today. Now, if we autopsy people, we find they are dying early of diseases of dietary excess. No one [in developed countries] is dying of dietary deficiency. … the last thing you need to worry about is deficiency. The only exception might be vitamins B12 and D.
• 1:01:39 [end of topic]

Notes from the book "The Pleasure Trap: Mastering the Hidden Force that Undermines Health & Happiness" by Dr. Lisle Ph.D. and Goldhamer 2003, chapter 6 Looking for Health in All the Wrong Places: Mental biases

• The cause in most modern-day health problems is dietary excess. The subtraction of these excesses will solve most health problems. Not the addition of medications or supplements.
• The threat of dying from starvation was an important problem for humans. Deficiency continues to be popular concept. Because that problem was an important factor in our evolutionary history. The human mind is naturally concerned with deficiency.
• The human brain is biased against accepting that dietary excesses are the root of most health problems. Because that problem was not a factor in our evolutionary history.

https://nutritionfacts.org/2011/09/12/dr-gregers-2011-optimum-nutrition-recommendations/
Dr. Greger's recommendations for Vitamin B12, Omega-3, Vitamin D, Calcium, Iodine, Iron, Selenium.