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(xiàng)新研究發(fā)現(xiàn)，黑巧克力和同類(lèi)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(guò)量攝入這兩種金屬會(huì)引發(fā)癌癥、慢性疾病或生殖和發(fā)育問(wèn)題，對(duì)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(zhǎng)的土壤中，因此無(wú)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(guò)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(yíng)養(yǎng)前沿》期刊上的研究指出，盡管有機(jī)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(yíng)養(yǎng)素類(lèi)黃酮、抗氧化劑和有益礦物質(zhì)而聞名，并被證實(shí)能改善心血管健康、認(rèn)知表現(xiàn)和減少慢性炎癥。

研究團(tuán)隊(duì)只檢測(cè)了純黑巧克力產(chǎn)品，因?yàn)樗鼈兊目煽桑次醇庸さ目煽稍梗┖孔罡?。含有其他成分的糖果或烘焙巧克力不在檢測(cè)范圍內(nèi)。研究沒(méi)有透露被檢測(cè)產(chǎn)品的名稱(chēng)或制造商。

這項(xiàng)新研究分析了72種巧克力產(chǎn)品中的鉛、鎘和砷含量。過(guò)往的研究只在某一特定時(shí)間點(diǎn)檢測(cè)了巧克力產(chǎn)品的重金屬含量，而這項(xiàng)新研究分別在2014年、2016年、2018年和2020年對(duì)巧克力產(chǎn)品進(jìn)行了檢測(cè)，時(shí)間跨度長(zhǎng)達(dá)8年。

研究人員發(fā)現(xiàn)，在研究過(guò)程中檢測(cè)的72種巧克力產(chǎn)品中，有43%超過(guò)了美國(guó)加州65號(hào)提案規(guī)定的鉛含量的上限值，有35%超過(guò)了該提案規(guī)定的鎘含量的上限值。該研究沒(méi)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(zhǎng)期攝入微量鎘元素會(huì)對(duì)腎臟造成損傷。美國(guó)環(huán)保署將鎘元素稱(chēng)為一種人類(lèi)致癌物。

世界衛(wèi)生組織表示，鉛是沒(méi)有安全攝入量的，尤其對(duì)兒童來(lái)說(shuō)。

世界衛(wèi)生組織在其官網(wǎng)上寫(xiě)道：“鉛尤其會(huì)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(huì)行為增加，以及學(xué)習(xí)成績(jī)退步?！?/p>

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