Dark chocolate and similar cocoa products are contaminated with lead and cadmium， two neurotoxic metals that are linked to cancer， chronic disease， or reproductive and developmental issues， especially in children， a new study found.

As natural elements in the Earth’s crust， lead， cadmium and other heavy metals are in the soil in which crops are grown and thus can’t be avoided. Some crop fields and regions， however， contain more toxic levels than others， partly due to the overuse of metal-containing fertilizers and ongoing industrial pollution.

However， despite growing on land with fewer pesticides and other contaminants， organic versions of dark chocolate had some of the highest levels， according to the study published Wednesday in the journal Frontiers in Nutrition.

Dark chocolate is known for being rich in plant nutrients called flavonoids， antioxidants and beneficial minerals and has been linked to improved cardiovascular health， cognitive performance and less chronic inflammation.

The research team examined only pure dark chocolate products as they contain the highest amount of cacao， the raw， unprocessed part of the cacao bean. Candies or baking chocolates with other ingredients were eliminated. The study did not disclose the names or manufacturers of the tested products.

The new study analyzed 72 consumer cocoa products for levels of lead， cadmium and arsenic. Compared with prior studies， which have looked at heavy metals in chocolate during a snapshot of time， the latest study tested the products over an eight-year period， in 2014， 2016， 2018 and 2020.

Of the six dozen chocolate products tested over the course of the study， 43% exceeded the maximum allowable dose level for lead as established by California’s Proposition 65， while 35% exceeded the Prop 65 maximum allowable level for cadmium， researchers found. The study found no significant levels of arsenic.

Over time， consuming low levels of cadmium can damage the kidneys. The Environmental Protection Agency calls the metal a probable human carcinogen.

There is no safe level of lead， especially for children， according to the World Health Organization.

“In particular， lead can affect children’s brain development， resulting in reduced intelligence quotient （IQ）， behavioural changes such as reduced attention span and increased antisocial behaviour， and reduced educational attainment，” WHO states on its website.

However， for healthy adults， risk analysis found little to worry about choosing to indulge in 1 ounce of dark chocolate now and again.

一項新研究發(fā)現(xiàn)，黑巧克力和同類的可可產(chǎn)品受到鉛和鎘這兩種神經(jīng)毒性金屬的污染。過量攝入這兩種金屬會引發(fā)癌癥、慢性疾病或生殖和發(fā)育問題，對兒童尤其有害。

作為地殼中的自然元素，鉛、鎘和其他重金屬存在于農(nóng)作物生長的土壤中，因此無法避免。然而，一些農(nóng)田和地區(qū)由于持續(xù)的工業(yè)污染和過度使用含金屬的肥料，其毒性水平比其他地區(qū)更高。

7月31日發(fā)表在《營養(yǎng)前沿》期刊上的研究指出，盡管有機黑巧克力產(chǎn)自農(nóng)藥和污染物較少的土壤，但是所含的幾種重金屬水平卻是最高的。

黑巧克力因富含植物營養(yǎng)素類黃酮、抗氧化劑和有益礦物質(zhì)而聞名，并被證實能改善心血管健康、認知表現(xiàn)和減少慢性炎癥。

研究團隊只檢測了純黑巧克力產(chǎn)品，因為它們的可可（即未加工的可可原豆）含量最高。含有其他成分的糖果或烘焙巧克力不在檢測范圍內(nèi)。研究沒有透露被檢測產(chǎn)品的名稱或制造商。

這項新研究分析了72種巧克力產(chǎn)品中的鉛、鎘和砷含量。過往的研究只在某一特定時間點檢測了巧克力產(chǎn)品的重金屬含量，而這項新研究分別在2014年、2016年、2018年和2020年對巧克力產(chǎn)品進行了檢測，時間跨度長達8年。

研究人員發(fā)現(xiàn)，在研究過程中檢測的72種巧克力產(chǎn)品中，有43%超過了美國加州65號提案規(guī)定的鉛含量的上限值，有35%超過了該提案規(guī)定的鎘含量的上限值。該研究沒有在這些巧克力產(chǎn)品中發(fā)現(xiàn)砷含量超標(biāo)的現(xiàn)象。

長期攝入微量鎘元素會對腎臟造成損傷。美國環(huán)保署將鎘元素稱為一種人類致癌物。

世界衛(wèi)生組織表示，鉛是沒有安全攝入量的，尤其對兒童來說。

世界衛(wèi)生組織在其官網(wǎng)上寫道：“鉛尤其會影響兒童的大腦發(fā)育，導(dǎo)致智商降低、行為改變，比如注意力下降和反社會行為增加，以及學(xué)習(xí)成績退步?！?/p>

不過，風(fēng)險分析發(fā)現(xiàn)，健康的成年人偶爾吃一點黑巧克力幾乎沒有什么可擔(dān)心的。