Which B vitamin is most important?

I'm going to echo what everyone else has said here and say: yes, they're all important. They're really not interchangeable, and it's a little bit silly that they're all grouped together when they're all so different.

But if I had to pick one, I'd pick B12.

It's the most common B vitamin deficiency, due to a combination of convoluted absorption pathway and low concentration in most modern diets.

Many well-intentioned vegetarians, vegans, and others on restricted diets have ended up crashing due to the anemia caused by B12 deficiency, which can take years to show up but can be very serious once it appears.

Most of my patients end up supplementing B12 at some point or another (especially the ones who don't want to eat beef liver, the highest food source of B12!)

B Vitamins need to be in balance so there's no one that's more important. Each B vitamin has specific jobs in the body for example B6 is great for hormone balance and B12 for liver detox. Taking a single B vitamin can cause deficiency in the other B vitamins. If one specific B vitamin is needed it can be taken individually along with a good quality B complex. If you don't know which one to take, a good range B complex can often help with energy and mood and won't create an imbalance. However it will turn your pee bright yellow, which is fine and normal.

It depends... Vegans and vegetarians who don't consume any animal products will eventually become deficient in B12 (cobalamin) and likely low in B6 (pyridoxine) and sometimes B9 (folate). People who consume a lot of alcohol become deficient in B1 (thiamine). And, those who subsist on fast food, sugar and caffeine will be deficient in many of the Bs and other nutrients as well. There are many nutrients in this family and they all have different jobs, but some of the main work they do is in protecting neurological tissue, helping to create energy, and promoting proper development of both red and white blood cells. Does everyone need to be on a B complex? No, but it is a good idea to have a nutrition expert read your lab results to see if you're in need of supplementation as many physicians miss early indicators. Can you have too much of a B vitamin? Absolutely. This is why it's important to work with someone who can help you determine what YOUR body needs. There are problems related to too much of a good thing as well as too little.

All B vitamins are vital for optimal health and wellness. Some of the B vitamins are more easily obtained through our regular diet. B vitamins are water soluble so they are not stored in the body long term. Include beans/peas, nuts/seeds, dark, leafy greens, and whole, unrefined grains. Eggs, dairy products and meat will complete the range of B vitamins your body needs. Many people choose to supplement with a B-Complex to make sure they are providing the body with what it needs and give them increased energy.
I would like the opportunity to discuss your personal needs or concerns. In wellness, Andrea