高铁质食物会提升运铁蛋白饱和度过高患者的癌症风险


  March 29, 2005 - 一项刊载于三/四月份家庭医学年监(Annals of Family Medicine)的世代研究结果显示,对于运铁蛋白过度饱和的患者,由食物中摄取过多的铁质会提升癌症的罹患风险。
  
  南卡罗莱纳医学院的Arch G. Mainous III指出,转铁蛋白饱和度超过60%,经证实是一项癌症的风险因素;至于转铁蛋白饱和度低于60%者,是否会因为在食物中摄取过高铁质而提升癌症风险,目前还不清楚。
  
  利用国家健康营养检验追踪调查(National Health and Nutrition Examination Survey I Epidemiologic)机构所提供的资料,研究人员对6309位美国成人进行追踪,追踪期从1971-1974到1992年,患者的基线年龄为25到74岁。
  
  患者中,有7.3%的基线血清转铁蛋白的饱和度超过45%,而摄取食物中的铁质和转铁蛋白的饱和度之间并无关连;相较于血清转铁蛋白饱和度正常且铁质摄取量较低者,饱和度超过45%且食物铁质摄取过高者,有著较高的癌症相关风险(2.24;95%可信度空间CI, 1.02 - 4.89)。
  
  转铁蛋白饱和度虽超过45%,但食物铁质摄取正常者,风险并未提高(危害比HR, 1.02,95%CI 0.69 -1.49);即使将转铁蛋白饱和度标准降低至41%,高转铁蛋白饱和度及高食物铁质摄取者的癌症相关风险仍然偏高(HR 2.00,95% CI,1.04 - 3.82)。
  
  Mainous表示,对于转铁蛋白饱和度过高的患者,每日摄取食物铁质若超过18mg,癌症风险就会提升;而饮食习惯改变是否有益于这些患者,是未来研究可能注重的议题。
  
  研究的限制因素,含铁质摄取量是由24小时的饮食纪录而来;食物铁质的总摄取量评估只进行了一次,而摄取量的纪录来自试验者的记忆,并非客观的测量;缺乏基线过后的饮食型态资料;某些癌症案例的确认方式,是根据死亡证书,患者自身或其家人对他人的叙述;无法对疾病的因果关系进行评估;高转铁蛋白饱和度;另外,食物铁质摄取过高者中,罹患癌症的人数相对过少。
  
  Mainous指出,根据目前的证据显示,如果美国人中有一大部分摄取了大量的食物铁质,他们引发不良后果的风险就会升高;虽然铁质过度缺乏会对健康产生严重的副作用,但是本项研究的数据突显了一个问题,那就是必须注意厂商在食物中添加铁质的对策。
  
  本研究的赞助单位,含Health Resources and Services Administration,及德拉维尔州公共健康部门。

High Dietary Iron in Patients<

By Laurie Barclay, MD
Medscape Medical News

March 29, 2005 — High intake of dietary iron in patients with elevated transferrin saturation increases the risk of cancer, according to the results of a cohort study published in the March/April issue of the Annals of Family Medicine.

"Transferrin saturation of more than 60% has been identified as a cancer risk factor," write Arch G. Mainous III, PhD, from the Medical University of South Carolina in Charleston, and colleagues. "It is unclear whether dietary iron intake increases the risk of cancer among individuals with transferrin saturation of less than 60%."

Using data from the National Health and Nutrition Examination Survey I Epidemiologic Follow-Up Study, the investigators followed 6,309 U.S. adults, aged 25 to 74 years at baseline, from 1971-1974 to 1992.

Serum transferrin saturation was more than 45% at baseline in 7.3% of the population. Intake of dietary iron was not correlated with transferrin saturation (r = .04). Compared with individuals who had normal serum transferrin saturation and low dietary iron intake, individuals who had serum transferrin saturation greater than 45% and high dietary iron intake had an increased adjusted relative risk of cancer (2.24; 95% confidence interval [CI], 1.02 - 4.89).

Individuals with a transferrin saturation of more than 45% but a normal dietary iron intake were not at increased risk (hazard ratio [HR], 1.02; 95% CI, 0.69 - 1.49). Even if transferrin saturation levels were set as low as 41%, the individuals with high transferrin saturation and high dietary iron intake would still have an increased adjusted relative risk of cancer (HR, 2.00; 95% CI, 1.04 - 3.82).

"Among persons with increased transferrin saturation, a daily intake of dietary iron more than 18 mg is associated with an increased risk of cancer," the authors write. "Future research might focus on the benefits of dietary changes in those individuals with increased serum transferrin saturation."

Study limitations include the use of a 24-hour dietary history to assess iron intake; assessment of exposure for total dietary iron made only once and by recall rather than objective measurement; lack of data on dietary patterns after baseline; ascertainment of cancer based on death certificates in some patients and on family or self-report in others; inability to assess causality; and relatively small number of individuals with high transferrin saturation and high dietary iron who developed cancer.

"The current evidence suggests that if a large proportion of the adult US population ingests high levels of dietary iron, then they have a significantly increased risk for deleterious consequences," the authors write. "Although severe iron deficiency causes serious adverse health effects, these data call into question the strategy of the addition of iron to food by manufacturers."

The Health Resources and Services Administration and the Delaware Division of Public Health helped support this study.

The authors report no conflicts of interest.

Ann Fam Med. 2005;3:131-137

Reviewed by Gary D. Vogin, MD

    
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