Low trace metal levels in American smokeless tobacco products mean no significant health risk
I previously discussed a comprehensive chemical analysis of smokeless tobacco products conducted by M.F. Borgerding and colleagues at RJ Reynolds Tobacco Co. and published in Regulatory Toxicology and Pharmacology. I focused on the results for tobacco-specific nitrosamines in that post.
Borgerding and colleagues analyzed many other agents, including trace metals. As they write, “Human exposure to toxic trace metals occurs from a variety of sources that include diet, the environment, vitamin and dietary supplements, tobacco and tobacco smoke, among others.” They measured levels of cadmium, arsenic, nickel, chromium and lead.
The diet is a prominent source of trace metals, so it is reasonable to compare the exposures to these metals from smokeless tobacco to those from the diet. I will use a series of reports from the European Food Safety Authority (EFSA) for these comparisons. I will report the metal levels in smokeless tobacco products as micrograms (ug) per gram (g) of tobacco, in dry weight. I will compare the exposure from using one can of moist snuff per day (about 15 g of tobacco, dry) with daily dietary exposure.
It is important to note that this discussion will deal only with exposure, which is the amount of a substance that is contained in food or other products that we consume. The other factor is uptake, which is the amount that we absorb. Substances have a broad range of absorption rates; the absorption rate from food traveling through the gastrointestinal tract may be different from that of a smokeless tobacco product held in the lip.
The absorption rate of trace metals from smokeless tobacco is not known, but a general idea is provided by studies that have estimated the percentage of nicotine absorbed from these products. A study that I discussed recently estimated that one-quarter to one-third of the nicotine in Swedish snus is delivered to the user. That is a good place to start with respect to the potential absorption of other agents.
Cadmium occurs naturally in the environment; for nonsmokers, the diet is the dominant source of this contaminant. It is potentially toxic to the kidneys, and is listed by the International Agency for Research on Cancer (IARC) as a carcinogen, primarily based on lung cancer after inhalation by workers in high-exposure industries (here).
The EFSA reports that dietary exposure is 19.5 ug. Borgerding reports that moist snuff contains cadmium at a level of 1.05 ug/g. Thus, a user of one can per day is exposed to 15.8 ug of cadmium, or about 80% of the dietary level. This combined exposure is only one-half of the 70 ug that the World Health Organization suggests as a safe daily cadmium intake.
A recent analysis of federal data revealed that smokeless tobacco users do not have elevated blood or urine cadmium levels compared with nonusers of tobacco. In that study cigarette smokers have elevated cadmium levels.
Arsenic also occurs naturally in the environment, and is present in a variety of forms. IARC lists arsenic as a cause of urinary bladder, lung and skin cancers, based on studies of high levels of the metal in drinking water (hundreds to thousands of ug per liter). The World Health Organization guideline recommends that level of arsenic in drinking water not exceed 10 ug per liter.
The EFSA reports that dietary exposure is 56 ug per day. Borgerding reports that moist snuff contains arsenic at a level of 0.21 ug/g, meaning that a one-can-per-day user is exposed to 3.2 ug of arsenic, or about 6% of the dietary exposure.
Nickel alloys and compounds have been produced commercially for over 100 years. IARC lists some nickel compounds as a cause of lung and nasal cancers, based on workers in these industries who were exposed to massive quantities by inhalation. In comparison, everyone else is exposed to vanishingly small quantities of nickel, mainly from food and water, and there is no evidence of health risks at this level.
The EFSA reports that dietary exposure to nickel is 150 ug/day. Borgerding observes that moist snuff contains nickel at a concentration of 2.05 ug/g. Thus, a one-can-per-day user is exposed to about 31 g, or roughly 21% of the dietary exposure.
As with nickel, metal workers who were exposed to massive quantities of some chromium compounds developed lung cancer, resulting in IARC classification of chromium as a carcinogen. However, there is little evidence that much lower exposure from food and water is problematic.
Chromium is, in fact, an essential micronutrient. The recommended daily allowance is 35 ug for adult men and 25 ug for adult women. Borgerding advises that moist snuff contains chromium at a concentration of 1.6 ug/g, so one can provides about 24 ug.
Lead occurs naturally in the environment, but exposures were elevated in the last century due to its use in water pipes, paint and gasoline. However, lead is no longer used for these purposes, making diet the primary source for most people. Because lead affects the developing nerve system, exposure among children is of particular concern. Although numerous studies have focused on workers exposed to massive quantities of lead, links to cancer are not conclusive; IARC lists lead as a probable carcinogen.
The EFSA reports that dietary exposure to lead is 41 ug/day. Borgerding notes that moist snuff contains lead at a concentration of 0.32 ug/g. A one-can-per-day user is exposed to about 6.1 ug, or 21% of the dietary exposure.
In summary, exposure to cadmium, arsenic, nickel, chromium and lead from moist snuff is much lower than that from a typical diet. Although all of these metals cause cancer in workers and others with massive exposures, levels from the diet and moist snuff are vastly lower and present no significant health risks.