補充鈣質並不會影響男性的血清脂質和體重
作者：Nancy Fowler
出處：WebMD醫學新聞
November 30, 2009 — 根據線上發表於11月11日美國臨床營養期刊(American Journal of Clinical Nutrition)的一篇紐西蘭研究，補充鈣質並不會如同改變女性般對年長男性的血清脂質或導致體重增減有所影響，但是可以改善飲食中缺乏此類礦物質者的血壓。
紐西蘭奧克蘭大學醫學與健康科學院醫學系的Ian R. Reid醫師等人寫道，許多臨床研究認為攝取鈣質對於血清脂質濃度有影響，特別是對女性的影響很明顯，人類和動物研究皆顯示，鈣及脂肪酸與腸道中的膽酸鍵結，造成脂肪吸收減少。
可能包括其他機轉，因為副甲狀腺素和1,25-dihydroxyvitamin D都有調節脂肪細胞的證據，在體外實驗中，前者在高濃度時可減少脂肪分解。這些效果也會導致減重，曾有報告指出與使用鈣質有關，許多觀察型研究也發現鈣質攝取與體重之間的關聯。
這項隨機控制試驗始於2004年，包括323名健康的40歲男性，服用安慰劑、每天600mg鈣、每天1200mg鈣。該研究的初級終點為，高密度脂蛋白(HDL)和低密度脂蛋白(LDL)膽固醇的改變比；次級終點為膽固醇分量和三酸甘油脂、血壓、身體組成的改變。
兩年後，研究對象在HDL/LDL比值上沒有顯著改變(P = .47)；研究者也發現，體重、脂肪或不含脂肪的體重、三酸甘油脂、整體LDL或HDL值並沒有改變(所有P = .28 )。有關HDL/LDL比值和三酸甘油脂，和之前的研究結果成對比，之前認為補充鈣質對於停經後婦女的血清脂質和體重有正面影響。
研究作者寫道，此研究認為補充鈣質對於男性的脂質代謝效果略小於女性。有關反應上的性別差異原因還不清楚。反之，睪丸酮對於膽固醇代謝有清楚的效果，這些與補充鈣質之間的交互作用是始料未及的。
飲食攝取鈣質低於平均值者(785 mg/天)之中，研究者指出在血壓有些微改變(接受每天1200鈣質者和安慰劑組在兩年時的改變P值分別是P = .05和 P = .06；收縮壓 –4.2 mm Hg；舒張壓 –3.3 mm Hg)。他們將這個改變歸因於鈣質的排鈉利尿效果，以及對副甲狀腺素和1,25-dihydroxyvitamin D的礦物質影響，這兩者都對血管平滑肌細胞有加壓效果。
研究作者並未報告研究限制，他們指出，此研究是有關鈣質對於男性體重之影響的最大型隨機試驗，其結果支持之前有關缺乏對體重之效果的發現。再者，他們指出，這個兩年期研究比之前的研究久，可以顯示出持續結果。
研究中發現血壓略為減少，雖然重要，但是並不足以提出廣泛使用鈣質作為高血壓的治療。
研究作者寫道，因此，我們的結論是，鈣質對於控制高血壓的治療價值可能是小的，且不足以證明將它例行性用於鈣質攝取量達平均水準之高血壓患者，不過，那些飲食攝取量低者可以考慮選擇性補充。
紐西蘭健康研究委員會以及Osteoporosis New Zealand公司資助本研究。由德州的Mission Pharmacal of San Antonio公司提供研究藥物。Reid醫師接受Mission Pharmacal提供對本研究的支持，他也擔任該公司的顧問。其他研究作者皆宣告沒有相關財務關係。
Am J Clin Nutr.線上發表於2009年11月11日。
Calcium Supplements Do Not Affect Men's Serum Lipids, Body Weight
By Nancy Fowler
Medscape Medical News
November 30, 2009 — Calcium supplements do not alter serum lipids or result in weight loss (or gain) in older men as they seem to do in women, but they can improve blood pressure in those whose diets are lacking in the mineral, according to a New Zealand study published online November 11 in the American Journal of Clinical Nutrition.
"The suggestion that calcium intake might have an effect on serum lipid concentrations has arisen from clinical studies, predominantly in women, and from human and animal studies showing that calcium binds to fatty acids and bile acids in the gut, which leads to reduced absorption of fat," write Ian R. Reid, MD, and colleagues in the Department of Medicine, Faculty of Medical and Health Sciences, at the University of Auckland in Auckland, New Zealand.
"Other mechanisms may also be involved, because there is evidence that both parathyroid hormone and 1,25-dihydroxyvitamin D regulate adipocyte activity, the former reducing lipolysis when present in high concentrations in vitro. These effects could also contribute to the weight loss that has been reported with the use of calcium and to the inverse association between calcium intake and body weight found in several observational studies."
The randomized controlled trial, begun in 2004, involved 323 healthy 40-year-old men who took a placebo, 600 mg of calcium daily, or 1200 mg of calcium daily. The study's primary endpoint was a ratio change of high-density lipoprotein (HDL) to low-density lipoprotein (LDL) cholesterol levels. Alterations in cholesterol fractions and triglycerides, blood pressure, and body composition were secondary endpoints.
After 2 years, the subjects showed no significant change in their ratio of HDL to LDL (P = .47). Researchers also found no modification of weight, fat or lean mass, triglycerides, or total LDL or HDL levels (P = .28 for all). The findings regarding HDL-to-LDL ratios and triglycerides contrast with the results of previous studies that suggest supplemental calcium has a positive impact on the serum lipids and body mass in postmenopausal women.
"This suggests that calcium supplements have a smaller effect on lipid metabolism in men than in women. The reason for a sex difference in response is not clear. Whereas testosterone clearly has effects on cholesterol metabolism, an interaction between these and the use of calcium supplementation is unexpected," the study authors write.
In subjects with dietary calcium intakes below the median value (785 mg/day), researchers did note slight changes in blood pressure (P = .05 and P = .06 for changes at 2 years in those who received 1200 mg of calcium per day vs placebo: systolic, –4.2 mm Hg; diastolic, –3.3 mm Hg). They attributed this alteration to the natriuretic effect of calcium and the mineral's impact on parathyroid hormone and 1,25-dihydroxyvitamin D levels, both of which have pressor effects on vascular smooth muscle cells.
The study authors have reported no limitations of the study. They noted that their study was the largest randomized trial of the effect of calcium on men's weight and that its results support previous findings regarding lack of effect on body mass. Furthermore, they stated that this 2-year study was longer than previous trials, which allowed it to show sustained results.
The slight decrease in blood pressure found in the study, though important, is not significant enough to warrant the widespread use of calcium as a treatment of hypertension.
"Thus, we conclude that the therapeutic value of calcium in managing hypertension is likely to be small and insufficient to justify its routine use in hypertensive subjects on average calcium intakes," the study authors write. "However, selective supplementation in those with low dietary intakes could be considered."
The study was supported by the Health Research Council of New Zealand and by Osteoporosis New Zealand. The study medication was provided by Mission Pharmacal of San Antonio, Texas. Dr. Reid has received research support for this study from Mission Pharmacal, for whom he has also acted as a consultant. The other study authors have disclosed no relevant financial relationships.
Am J Clin Nutr. Published online November 11, 2009.
