Vitamin B12 deficiency can occur despite a seemingly adequate diet due to several reasons:

1. Malabsorption Issues: One of the most common reasons for vitamin B12 deficiency is malabsorption. This can happen if your stomach lining is not producing enough intrinsic factor, a protein necessary for vitamin B12 absorption. Conditions like pernicious anemia result in the immune system attacking cells that produce intrinsic factor¹.

2. Gastrointestinal Disorders: Issues like gastritis, celiac disease, or the use of certain medications (such as proton pump inhibitors) can interfere with the absorption of vitamin B12². These conditions reduce the stomach's ability to produce hydrochloric acid and release B12 from proteins in foods³.

3. Prolonged Use of Certain Medications: Some medications can interfere with vitamin B12 absorption. These include antacids and metformin, often used in diabetes management³.

4. Dietary Insufficiency: Although your diet seems adequate, the vitamin B12 from animal sources needs to go through a two-step absorption process, which can be compromised⁴.

In your case, even with a decent intake of B12-rich foods, malabsorption could be the main issue. Supplements, particularly in forms like tablets, sublingual (under the tongue), or injections, might be beneficial because they generally don't require the same digestive processes to be absorbed⁴. These forms can be absorbed more effectively in cases where intrinsic factor or stomach acid production is inadequate.

Your doctor has started you on supplements, which can be very effective in correcting deficiencies, especially if malabsorption is the cause³. It might be beneficial to reevaluate your B12 levels after a period of supplementation to ensure levels are improving.

Whether you can stop taking vitamin B12 supplements in the future depends on the underlying cause of your deficiency. Here are some scenarios to consider:

1. Pernicious Anemia: If your deficiency is due to pernicious anemia—an autoimmune condition affecting intrinsic factor production—you will likely need lifelong vitamin B12 supplementation¹. Pernicious anemia does not go away with time, so ongoing management with supplements or injections is typically necessary².

2. Temporary Malabsorption: If your deficiency is due to a temporary issue, such as a reversible gastrointestinal condition or medication that you can stop taking, you might be able to reduce or stop supplementation after resolving the underlying issue³. Regular monitoring of your B12 levels would be essential in this case to ensure your levels remain adequate.

3. Dietary Insufficiency: If the deficiency stemmed from inadequate dietary intake, improvements in your diet combined with monitoring might allow you to reduce reliance on supplements once levels are normalized⁴.

4. Use of Certain Medications: If medications that cause malabsorption (like proton pump inhibitors or metformin) are discontinued, absorption might improve, potentially allowing you to reduce supplementation⁵. Again, monitoring your levels would be crucial.

It's important to maintain regular check-ups with your healthcare provider to assess your vitamin B12 levels and adjust your supplementation strategy accordingly. Your healthcare provider may advise periodic blood tests to monitor your status and ensure you remain at a healthy level of B12.