Nutrients. 2015 Jan; 7(1): 552–571.  Published online 2014 Jan 14. doi:  10.3390/nu7010552 PMCID: PMC4303853  Dietary Strategies for the Treatment of Cadmium and Lead Toxicity - Qixiao Zhai,1 Arjan Narbad,2 and Wei Chen1,3,*

4. Edible Plants and Dietary Phytochemicals

Vegetables, fruits and other edible plants are important dietary sources of vitamins and essential metals. Edible plant supplementation at sufficient levels can promote the levels of the vitamins and essential metals in the human body, which in turn can decrease the risks of Cd and Pb toxicity. Moreover, edible plants provide a great variety of other nutrients, such as dietary protein and phytochemicals, which have been reported to have beneficial effects against Cd and Pb toxicity (Table 2 and Table 3).

A selection of studies on the protective effects of edible plants against Cd and Pb toxicity is presented in Table 2.

Soybean for example has been a part of the Southeast Asian diet for millennia. Two recent animal studies showed that dietary soybean supplementation helped to prevent arterial and cardiac injury by alleviating the oxidative stress induced by Cd toxicity. The authors suggested that the soybean protein and soybean isoflavones provided the observed antioxidant effects.

Garlic, ginger and onion are used as ingredients for flavour, aroma and taste enhancement all over the world. Garlic is also a well known medicinal plant. Garlic extract alleviates Pb-induced neural, hepatic, renal and haematic toxicity in rats and protects against Cd-induced mitochondrial injury and apoptosis in tissue culture models. Based on these studies, garlic’s protective property against Cd and Pb toxicity can be attributed to

 (1) its antioxidative ability, provided by organo-sulphur compounds such as diallyl tetrasulfide;

 (2) its chelation ability, provided by sulphur-containing amino acids and compounds with free carboxyl and amino groups, which in turn promotes the excretion of Pb or Cd from the body; and

 (3) the prevention of Cd and Pb intestinal absorption, by its sulphur-containing amino acids such as S-allyl cysteine and S-allyl mercaptocysteine.

Ginger and onion have similar antioxidant capacities to garlic, and supplementation with these food ingredients gave protection against Pb-induced renal and developmental toxicity and Cd-induced gonadotoxic and spermiotoxic effects in rats.

Green tea and curry leaves are commonly used in Asian cooking and are endowed with numerous potential benefits to human health including alleviating the oxidative stress induced in diabetes and protecting liver from ethanol induced toxicity. These plants are also gaining popularity in the West. The protective effect of green tea against Cd and Pb toxicity is mainly due to its active constituent, catechins, which are discussed later in this section. The flavonoids and phenols in curry leaves can function as antioxidants and as potential chelators, which offer protection against Cd-induced cardiac toxicity.

Fruits such as grapes are also effective against Cd toxicity. Besides the function of vitamins and essential metals in grapes, the abundant polyphenols such as anthocyanins may also alleviate the oxidative stress caused by Cd and Pb toxicity.

Tomato is regarded as one of the most powerful natural antioxidants and can prevent renal toxicity induced by Pb exposure in rats. Moreover, tomato has been reported to produce metal chelating proteins and phytochelatins when exposed to heavy metal ions. In fact the oral administration of tomato has been shown to significantly reduce the accumulation of heavy metals (Cd, Pb and Hg) in the liver of rats [88].

Other plants, such as

• ginseng (Panax ginseng Meyer),
• liquorice (Glycyrrhizae radix),
• torch ginger (Etlingera elatior)  and
• tossa jute (Corchorus olitorius)

are also reported to have protective effects against Cd and Pb toxicity. Some of these plants such as tossa jute (used as a vegetable and food ingredient common to the people of Eastern Asia and Africa) or torch ginger (used in Malaysian local dishes) are popular dietary components in certain areas, whereas the others are routinely added in in candies and beverages (such as liquorice). They can therefore be recommended as dietary supplements for the prevention and alleviation of heavy metal intoxication to populations that are at risk of heavy metal exposure and who regularly consume these plants.

Some studies designed to explore the protective mechanisms have investigated the effects of specific plant-derived phytochemicals against Cd and Pb toxicity, rather than the intact plant itself. Table 3 presents a selection of related phytochemicals, their protective mechanisms and their food sources. Most of these phytochemicals are phenolic or isoflavone in nature and are found in commonly consumed fruit and vegetables. These bioactive compounds can act as oxygen free radical scavengers or metal chelators, which enables them to be used as natural antagonists to Cd and Pb toxicity.