DEAR DR. BLONZ: I have pernicious anemia, for which I receive B12 injections. Why is it that intrinsic factor cannot be synthesized and introduced into the body by injection or pills? It seems as though that would be better. -- T.D., Anderson, South Carolina

DEAR T.D.: As you know, but other readers may not, two separate components are needed for vitamin B12 to be absorbed. The first is the vitamin itself, and the second is a protein manufactured by the body that is called the “intrinsic factor.” That factor links with vitamin B12 and provides the escort that carries it through the absorptive surface of the intestines. Without its intrinsic factor, little, if any, vitamin B12 would ever get into your system.

Pernicious anemia, which only occurs in about 2% of individuals, is when the stomach produces an insufficient amount of that intrinsic factor protein. When this is the case, dietary sources of vitamin B12 do not get absorbed. We cannot get the same effect from taking intrinsic factor as a dietary supplement, as it will get broken down like other nutritional proteins.

To date, the most workable treatment for pernicious anemia is the periodic injection of the preformed vitamin B12. The strategy should be worked out with your health professional, who can help identify factors or medications that may be involved. I encourage you to discuss whether your situation is one where alternatives might be available, such as elevated oral doses of vitamin B12, or ones administered as a sublingual tablet, nasal gel or spray.

Check out the additional discussion at the National Institutes of Health at b.link/pernicious.

DEAR DR. BLONZ: A lady in my office says that she was told the calcium in milk is the wrong kind for our bodies, and is not easily absorbed. Since she is pregnant, I’d like to be sure this is correct, so she’s not ignoring something important. Is there any truth to this? -- M.M., Phoenix, Arizona

DEAR M.M.: No. The idea that the calcium in milk is the “wrong kind” is without merit.

There are many types and dietary sources of calcium. Dairy products represent an excellent and convenient source. One advantage is that the body absorbs a higher percentage of dairy calcium than calcium carbonate, which is a common form of calcium found in dietary supplements.

A key consideration here is that while calcium is essential -- especially for a mother and her developing child -- dairy products are not.

Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: I’m a 69-year-old male, vegan, with an active cycling routine. For most of my adult life, I’ve been a blood donor without any problems. About two years ago, I began consistently failing the initial screen due to low blood iron. Eventually, one of the technicians asked if I drank tea. I had, in fact, begun drinking tea daily around the time I began failing the blood screen. A few weeks ago, after abstaining from tea for a few days, I passed the screen and successfully donated.

My online research seems inconclusive about whether tea depletes iron. I would have thought that low blood iron would seriously affect my cycling performance, but I haven’t seen definite signs of that. To what extent does tea deplete blood iron? Will drinking a cup or two of tea per day affect endurance and athletic performance? -- S.H., Tulsa, Oklahoma

DEAR S.H.: My compliments to you, and all who are blood donors; it is a generous pay-it-forward way to give of ourselves, and help others in a way unlike any other.

Donation centers don’t typically measure blood iron directly; what they screen for is the level of hemoglobin, the iron-containing “metalloprotein” in red blood cells designed to carry oxygen. Blood accounts for about 10% of body weight, about 1.2 to 1.5 gallons, and the amount removed during the donation should only have a minimal, short-term impact on the oxygen-carrying ability of a donor’s blood. We have extra blood stored in the spleen, so the blood volume is rapidly replenished. For more on donations, see b.link/donor.

Kudos also on your healthful approach, and to your detective work in having tea on the suspect list. Teas made from black tea leaves, and to a lesser extent, oolong, then green, contain tannins that can bind with minerals such as iron and affect their absorption. This is not tea depleting body iron; it is the tannins affecting absorption, so dietary iron is less able to make it in. (I realize this might seem odd, but for physiological reasons, the digestive tract is often considered to be outside of the body; it’s only after a substance is absorbed that it is considered “in.”) Think of the tannin effect as a physical phenomenon within your digestive system, where the tannins are binding with the mineral to form a compound that is too large to be absorbed.

Your experience with a brief cessation of tea drinking and with your cycling would suggest that this may only be a minor issue. You could counter the effect by avoiding drinking high-tannin teas with iron-rich meals. (There is a list of vegetarian sources of iron at b.link/zr38h.)

I do recommend you relate these experiences to your health professional to help decide if a more informative blood test would be indicated.

Finally, tea has several healthful benefits, so enjoy. There are teas with low, or no tannins, and certain herbal teas are tannin-free.

Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: I was looking up information on juicing “prescriptions” for arthritis and other maladies, but I found different information on different sites. These were mainly commercial sites, and many included customer testimonials. Is there anything consistent on the research side of this topic? -- J.F., New Rochelle, New York

DEAR J.F.: The lack of research to provide a scientific basis for “juice prescriptions” opens the door for an advice free-for-all. One site might endorse pineapple juice for arthritis; another pushes broccoli, kale and spinach; and yet another recommends celery, cherry, bean sprouts, carrots and cucumbers. While such foods all have nutritious attributes, prescribing them for specific ailments is a dubious proposition. (Testimonials are not objective evidence.)

Unfortunately, the focus on curing specific diseases overshadows the value of juicing. It’s a bit shocking that in 2018, soft drink consumption in the U.S. averaged about 38 gallons per person (see b.link/pce8f). Our bodies would be better off if we got our refreshment from water, or fresh vegetable or fruit juices, instead. Not only do juices have wonderful flavors, they also contain valuable nutrients not available in soft drinks. For example, a 6-ounce glass of fresh carrot juice contains only 73 calories and is loaded with healthful phytochemicals. Fresh apple, pineapple or melon juices yield flavors and aromas unmatched by any other beverage.

The beneficial effects of eating more fruits and vegetables are not disputed. And it’s a lot easier to drink a pound of carrots than to eat the same amount of vegetables. But because juice doesn’t have fiber and other solids, the goal should be to have juice in addition to, not instead of, fresh fruits and vegetables. And, although proponents of juicing might swear you get all the essential goodness (except the fiber), it’s unclear what proportion of the nutrients are left behind when the pulp is not included.

There are three basic types of juicers. Extractors, the most popular kind, grind the food with a high-speed spinning dish that traps the pulp. They often have an ejector that deposits the pulp in a convenient bin. Masticator-type juicers “chew up” the food at a slower speed and make juice by mechanically pressing the ground-up produce against a screen. Finally, there are specialized blender/juicers that grind the entire fruit or vegetable. This is the one type of machine that doesn’t remove the pulp, and as a result, juices from these machines retain the food’s fiber. The tradeoff, however, is that the output can end up as slush rather than juice.

Here are some tips for the juicer-to-be:

-- Taste a range of fresh juices before you spend money on a juicer. Find a juice bar in your area, or arrange for a demonstration so that you can sample a variety of freshly made juices. Make a note of the juicing method used.

-- When shopping for a juicer, find a model that’s easy to clean. If cleaning is a bother, the machine is likely to sit unused.

-- To avoid any possible digestive problems, don’t overdo it at first. Introduce new fruits and vegetables gradually.

Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.