Q. I've been told I should take extra folic acid to prevent heart disease, but I don't know how much to take. What do you recommend?
A. You were probably told this because folic acid can lower elevated homocysteine, which is a risk factor for heart disease. How much to take is a good question.
Certainly it is important to take enough to bring homocysteine down to normal levels—less than 8 nmol/ml is considered optimal. If you haven't had your homocysteine measured to know whether it is normal, a recent article suggests that daily doses of at least 800 mcg of folic acid are required to achieve the maximal reduction in homocysteine concentrations.1 Keep in mind, when you take supplemental folic acid, you should always take vitamin B12 with it, as folic acid can mask a B12 deficiency, although this is rare.
In fact, you should add vitamin B12 to your efforts. Many health care professionals only think of folic acid when trying to deal with elevated homocysteine. However, one study showed that 17 percent of patients who had a vitamin B12 deficiency (defined as B12 levels less than 258 pmol/L) along with a homocysteine level greater than 14 mumol/L also had increased amounts of carotid plaque, suggesting that there is a relationship between B12 and risk of cardiovascular disease.2 How much B12 should you take to avoid potential problems? One study looked at older individuals with low vitamin B12 levels and found they needed 500 mcg daily to bring them up to the normal range.3 Even though this dose is based upon older individuals, it also seems reasonable for younger people—just to be on the safe side.
There is no known toxicity of either folic acid or B12 at these levels. A good-quality multiple vitamin should include both. By taking a multiple, you will also get vitamin B6 (best at around 10 to 25 mg/day), which is also important in lowering homocysteine. All three of these B vitamins should be part of any homocysteine-lowering regime.
Q. I've heard that I should include watercress in my diet if I want to decrease my risk of cancer. Is this true?
A. Watercress (Nasturtium officinale) is a wonderful addition to salads and is also good cooked. The vegetable is a member of the crucifer family, which includes broccoli, cauliflower and kale. All crucifers contain high levels of glucosinolates, which when consumed either cooked or uncooked are converted to isothiocyanates like phenylethyl isothiocyanate. Isothiocyantes are sulphur-containing phytochemicals that appear to make crucifers of special benefit.4,5,6,7
PEITC has been shown to inhibit chemically induced lung and colon carcinogenesis in rats and to promote the excretion of carcinogens in humans.8,9 Thus the glucosinolates in watercress and other crucifers appear to improve our ability to detoxify and excrete certain environmental carcinogens, and are one of the proposed reasons crucifers like watercress may be chemoprotective.10,11
Q. I seem to be losing my sense of taste. Do you know what may help?
A. There are many reasons for losing your sense of taste, and a zinc deficiency may be one of them. Zinc is an essential mineral and is required for normal taste and smell, among other functions. Unfortunately, as we age it becomes harder to digest and absorb minerals such as zinc. In addition, through a less-than-adequate diet, we often just don't get enough of this important mineral. Studies suggest that some people low in zinc may benefit from zinc supplementation to improve taste sensation. For instance, loss of taste is a common side effect with some chemotherapy drugs, and a zinc deficiency is postulated to be associated with this development. A number of trials looking at taste loss in people undergoing cancer treatment have shown that supplementing with zinc can, for some people, help taste sensation,12,13,14 although not all studies have been positive.15 It does seem reasonable that you try 30 to 45 mg/day of zinc. After two to three months, if there is no change, it is unlikely that this additional zinc will help, and you should discontinue the supplementation.
1. [no authors] Dose-dependent effects of folic acid on blood concentrations of homocysteine: a meta-analysis of the randomized trials. Am J Clin Nutr 2005;82(4):806-12.
2. Robertson J, et al. Vitamin B12, homocysteine and carotid plaque in the era of folic acid fortification of enriched cereal grain products. CMAJ 2005;172(12):1569-73.
3. Eussen SJ, et al., Oral cyanocobalamin supplementation in older people with vitamin B12 deficiency: a dose-finding trial. Arch Intern Med 2005;165(10):1167-72.
4. Getahun SM and Chung FL. Conversion of glucosinolates to isothiocyanates in humans after ingestion of cooked watercress. Cancer Epidemiol Biomarkers Prev 1999;8(5):447-51.
5. Krul C, et al. Metabolism of sinigrin (2-propenyl glucosinolate) by the human colonic microflora in a dynamic in vitro large-intestinal model. Carcinogenesis 2002;23(6):1009-16.
6. Chung FL, et al. Quantitation of human uptake of the anticarcinogen phenethyl isothiocyanate after a watercress meal. Cancer Epidemiol Biomarkers Prev 1992;1(5):383-8.
7. Rouzaud G, et al. Hydrolysis of glucosinolates to isothiocyanates after ingestion of raw or microwaved cabbage by human volunteers. Cancer Epidemiol Biomarkers Prev 2004;13(1):125-31.
8. Hecht SS. Chemoprevention of cancer by isothiocyanates, modifiers of carcinogen metabolism. J Nutr 1999;129(3):768S-74S.
9. Chung FL, et al. Chemoprevention of colonic aberrant crypt foci in Fischer rats by sulforaphane and phenethyl isothiocyanate. Carcinogenesis 2000;21(12):2287-91.
10. Talalay P and Fahey JW. Phytochemicals from cruciferous plants protect against cancer by modulating carcinogen metabolism. J Nutr 2001;131(11 Suppl):3027S-33S.
11. Keck AS and Finley JW. Cruciferous vegetables: cancer protective mechanisms of glucosinolate hydrolysis products and selenium. Integr Cancer Ther 2004;3(1):5-12.
12. Ripamonti C, et al. A randomized, controlled clinical trial to evaluate the effects of zinc sulfate on cancer patients with taste alterations caused by head and neck irradiation. Cancer 1998;82(10):1938-45.
13. Sakai F, et al. Double-blind, placebo-controlled trial of zinc picolinate for taste disorders. Acta Otolaryngol Suppl 2002(546):129-33.
14. Yamagata T, et al. The pilot trial of the prevention of the increase in electrical taste thresholds by zinc containing fluid infusion during chemotherapy to treat primary lung cancer. J Exp Clin Cancer Res 2003;22(4):557-63.
15. Matson A, et al., Zinc supplementation at conventional doses does not improve the disturbance of taste perception in hemodialysis patients. J Ren Nutr 2003; 13(3):224-8.
Natural Foods Merchandiser volume XXVII/number 3/p. 128