Q: I've heard that spinach and some other vegetables contain significant amounts of oxalic acid, which can interfere with absorption of some minerals. What do you think about the oxalic acid issue?
A: Oxalic acid is a natural product found in spinach and some other plant foods including rhubarb. (Levels are so high in rhubarb leaves that we don't eat them — they're poisonous.) It imparts a sharp taste to beet greens and chard that I don't like, especially in older leaves. Concentrations of oxalic acid are pretty low in most plants and plant-based foods, but there's enough in spinach, chard and beet greens to interfere with the absorption of the calcium these plants also contain. For example, although the calcium content of spinach is 115 mg per half-cup cooked, because of the interference of oxalic acid, you would have to eat more than 16 cups of raw spinach or more than eight cups of cooked spinach to get the amount of calcium available in one cup of yogurt.
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However, the oxalic acid in vegetables is broken down in cooking and doesn't interfere with the absorption of calcium present in other foods, cheese for instance, that you might eat at the same time. Calcium is available from many other food sources — in addition to yogurt, cheese and milk (there's slightly more of the mineral in nonfat milk than in any other type), it is also found in a wide variety of fortified foods, including orange juice, soy milk and cereals.
I certainly wouldn't avoid spinach or other leafy greens because of the oxalic acid effect. Spinach has a lot to offer nutritionally: It's an excellent source of folic acid, potassium and magnesium, as well as vitamin K, carotenes, vitamin C and lutein, important for healthy eyes.
As far as calcium is concerned, I recommend that women aim for a total daily calcium intake of 1,000 to 1,200 mg per day from all sources, including supplements of 500 to 700 mg of calcium citrate in two divided doses taken with meals. For men, I now suggest aiming for 500 mg from all sources. And unless they are getting almost no calcium from food, men should not supplement with calcium — high intake has been linked to an increased risk of prostate cancer.
Q: Is there now a cure for Alzheimer's disease? I heard a report about a drug that reversed symptoms within minutes. True? If so, what can you tell me about it?
A: I wish there were a cure for Alzheimer's disease, but we're not there yet.
The report you heard described a case study at UCLA in which an 81-year-old patient with Alzheimer's was treated with the drug etanercept, better known as Enbrel, which is FDA-approved for the treatment of rheumatoid arthritis and a few other autoimmune diseases. In a study published in the Jan. 9, 2008, issue of the Journal of Neuroinflammation, UCLA researchers reported on the patient's dramatic improvement within minutes after etanercept was injected into his neck. Cognitive tests before and after treatment documented the change.
This isn't the first time this extraordinary effect has been noted. In 2006 the same authors reported on a six-month pilot study including 15 patients who were treated with the drug and improved within minutes. They also claim the immediate benefit has been sustained with continued treatment.
The drug appears to work via its effect on tumor necrosis factor-alpha (TNF), a soluble protein (cytokine) in the brain that normally regulates transmission of nerve impulses. The investigators hypothesized that excess TNF-alpha found in Alzheimer's patients interferes with this regulatory process. Etanercept binds and inactivates excess TNF, apparently bringing about the improvement.
This is a very exciting development for the insight it provides into the brain changes that underlie Alzheimer's and how some of them could be addressed. However, TNF-alpha isn't the only factor involved in the disease, and it would be a mistake to assume that the new study gives us the answer to reversing Alzheimer's.
It is the most encouraging development I've seen, though, and I look forward to seeing larger studies.