Organic vs. Conventional: The Overlooked Low Cadmium Advantage. Almost 50% Lower Cd Levels and Half-Lifes of 10-30 Years May Be Another Reason to Buy Organic

Eating organic is not so much about what you get extra (vitamins etc.), but rather about paying more for getting less. Less pesticides and, as recent studies show, significantly less cadmium.

In view of the hype around organic produce, it would appear as if this was a bogus question, but previous studies were not able to confirm any of the huge claims you will read all over the internet. The only established benefit so far - and that's certainly not one you should underestimate - appears to be a relative lack of pesticides.

Only recently scientists have compared a broad variety of organic and conventially grown crops and found that organically grown crops do tend to have a notably lower cadmium content, as well. According to  conventionally grown crops – on average, about 48 % lower (this estimate takes into account 87 previously reported comparisons).
In view of the fact that the heavy metal cadmium (Cd) is emerging as a major cause of vascular disorders, various common cancers, kidney disease, osteoporosis and other health disorders, even in populations that do not have occupational exposure to this toxin(2–4), this is significant news.

With the exception of smokers, who are constantly exposed to significant amounts of cadmium, green vegetables, root vegetables, tubers, grains, organ meats and shellfish are the major sources of this toxin. Any reduction of the Cd levels in these foods may thus have significant beneficial health implications, since once Cd gets into your body, it cannot be excreted again.

Scientists estimate the half-life of cadmium in the human body to be 10–30 years (Suwazono. 2009)! Thus every nanogram you don't consume counts!

While cadmium can induce oxidative stress throughout the body, and interference with some of the physiological roles of Zn (as in DNA repair), the evidence that dietary (not smoke) exposure to cadmium has significant health effects is yet scarce.
This is partly due to the fact, though, that our ability to measure the chronic effects of very low doses of a certain toxic substance are very limited. In a recent review, McCarthy et al. (2014) list the following hitherto published studies:

• Table 1: Whether there are more or less antioxidants in organic produce depends on the antioxidant you're looking at (Barański. 2014)

  Japanese researchers have long speculated about an involvement of cadmium exposure in the development of breast cancer and researchers from all around the world have speculated based on elevated urinary Cd concentrations that it may be responsible for 27-68% of the breast cancer cases (McElroy. 2006; Gallagher. 2010; Nagata. 2013).
• Recent multivariate-adjusted analyses of the National Health and Nutrition Survey cohort have concluded that Cd exposure may be responsible for 28 % of the myocardial infarction cases and 17 % of the total CVD and cerebrovascular disease cases (Everett. 2008; Agarwal. 2011). And data from the prospective Strong Heart Study (focusing on Native Americans) suggest that Cd exposure may account for 16, 23 and 28 % of the coronary disease, stroke and heart failure cases, respectively (Tellez-Plaza. 2013).

In spite of the fact that the epdidemiological evidence is not exactly abundant and disregarding the null results of case-control studies attempting to correlate dietary Cd intake with disease risk McCarthy et al. conclude that "if one focuses on urinary Cd concentrations when surveying Cd epidemiology, the hazard of Cd stands out crystal-clear" (McCarthy. 2014).
References:

• Agarwal, Shikhar, et al. "Heavy metals and cardiovascular disease: results from the National Health and Nutrition Examination Survey (NHANES) 1999-2006." Angiology 62.5 (2011): 422-429.
• Barański, Marcin, et al. "Higher antioxidant and lower cadmium concentrations and lower incidence of pesticide residues in organically grown crops: a systematic literature review and meta-analyses." British Journal of Nutrition 112.05 (2014): 794-811.
• Everett, Charles J., and Ivar L. Frithsen. "Association of urinary cadmium and myocardial infarction." Environmental research 106.2 (2008): 284-286.
• Gallagher, Carolyn M., John J. Chen, and John S. Kovach. "Environmental cadmium and breast cancer risk." Aging (Albany NY) 2.11 (2010): 804. 
• Gallagher, Carolyn M., John J. Chen, and John S. Kovach. "The relationship between body iron stores and blood and urine cadmium concentrations in US never-smoking, non-pregnant women aged 20–49 years." Environmental research 111.5 (2011): 702-707.
• McCarty, Mark F. "Zinc and multi-mineral supplementation should mitigate the pathogenic impact of cadmium exposure." Medical hypotheses 79.5 (2012): 642-648.
• McCarty, Mark F., and James J. DiNicolantonio. "Are organically grown foods safer and more healthful than conventionally grown foods?." British Journal of Nutrition 112.10 (2014): 1589-1591.
• McElroy, Jane A., et al. "Cadmium exposure and breast cancer risk." Journal of the National Cancer Institute 98.12 (2006): 869-873. 
• Nagata, Chisato, et al. "Cadmium exposure and the risk of breast cancer in Japanese women." Breast cancer research and treatment 138.1 (2013): 235-239.
• Suwazono, Yasushi, et al. "Biological half-life of cadmium in the urine of inhabitants after cessation of cadmium exposure." Biomarkers 14.2 (2009): 77-81.
• Tellez-Plaza, Maria, et al. "Cadmium exposure and incident cardiovascular disease." Epidemiology 24.3 (2013): 421-429.