Low-Level Cadmium Exposure and Bone Health

To the Editor: We thank Maria Wallin and colleagues1 for sharing their significant study about how low-level cadmium exposure through diet and smoking can increase the risk of low bone mineral density (BMD) and osteoporosis-related fractures in elderly men. The data came from the Swedish cohort of the Osteoporotic Fractures in Men (MrOS) study. The researchers used cadmium in urine (U-Cd) as an index of body cadmium burden after cadmium exposure, and the mean U-Cd level was 0.33 (median 0.26, range 0.01 to 6.98) µg/g creatinine. They also made a statistic on the calcium intake (range 60.7 to 4140 mg/d) of the participants. However, there are some concerns with this study. First, the mean U-Cd level of the subjects included in this study was 0.33 µg/g creatinine, and the U-Cd ranged from 0.01 to 6.98 µg/g creatinine, which means that the U-Cd levels in some subjects were >5.00 µg/g creatinine. According to the World Health Organization (WHO) standard, the reference levels of U-Cd are 2 µg/g creatinine for environmental exposure, 5 µg/g creatinine for occupational exposure, and 10 µg/g creatinine for possible renal impairment caused by cadmium.2 So, when the U-Cd levels of the subjects were >5.00 µg/g creatinine, the researchers should consider the possibility of contamination or occupational exposure. We suggest that the authors should remove the subjects whose U-Cd levels were >5.00 µg/g creatinine out of the group and should not be used as the low-level cadmium-exposed population. Moreover, calcium intake is an important risk factor for osteoporosis. According to the National Osteoporosis Foundation (NOF), the recommended daily intake of calcium for men aged 50 to 70 years is 1000 mg, whereas for those aged 71 years and older is 1200 mg; this dosage is expected to help reduce fracture risk and minimize the risk of osteoporosis in adulthood.3 Therefore, in the same level of cadmium exposure, people with higher calcium intake may have lower risk in osteoporosis and fractures than those with lower calcium intake. We suggest that the subjects should be divided into two groups of high-calcium intake group and low-calcium intake group and to better show whether calcium would produce the protected effect on cadmium exposure. The authors state that they have no conflicts of interest.