I'm a liver lover too. I bring some home, my dog goes nuts and my wife gives me one of those 'what have you done' looks and promptly leaves. She hates it. And strangely don't know anyone else you enjoys the livery pleasure. Fry up a big pile of onions in butter for at least 30 minutes, flash fry the liver and you have a mighty fine nutritious meal. S&P, splash of balsamic vinegar. Caramelised onions and liver, marvellous. For non liver lovers a great intro into the delights of liver.....it actually doesn't taste much of liver, less livery than a good pate. Maybe it's the texture thing, I dunno.
Deficiency? I really don't know.....your body might be telling you something, perhaps? Certainly often touted as the most nutritious food going, or one of anyway. I generally go for lamb's liver. If you know where your liver comes from then you can make assumptions of its health.....not sure about beef liver....older cattle, antibiotics, grass v grain doubts. Probably more important than steak or any meat cut when you consider liver as an organ, what it does etc and what has been through it. Lamb is a good option.....youth and grass fed. And very yummy. There is some doubts about how much you should eat, such is the nutrient density of vitamin A, you can get too much. Dunno what that is though. I go for once a week or so with pate in a salad now and then too. Easy to make your own pate too.
You should see the piles of saliva left by my dog when I walk in with liver and bone marrow! They know, you know.....