Many consider milk to a healthy addition to a diet. There have been entire marketing campaigns — Got Milk? — advocating adding cow's milk to the diets of young children, frail elderly and athletes. In recent years, marijuana is also considered by many to be a healthy addition — not to a diet, but as treatment for many diseases.

Milk and marijuana have more in common than just potential health benefits. Both can be damaging to health when contaminants are introduced into the final product. And both have had high levels of pesticides identified in a supposedly healthy product. If the person consuming the product is from a segment of the population that is particularly vulnerable such as developing children or neurologic impaired adults, the outcome can be serious.

In a 2014 study of milk obtained from a market in Greece, 97 percent of the samples contained evidence of pesticides, although the majority were within the range considered acceptable. The researchers analyzed the risk to a child drinking the milk, taking into consideration age and weight, and determined the risk was below standards set by the United States and the World Health Organization.

Products contaminated with pesticides are harmful to developed brains as well as those still undergoing growth and development. This was demonstrated in study of older adults who had consumed pesticide-contaminated milk in their middle-age years.

The milk supply in Hawaii had been identified to have high levels of pesticides during the early 1980s. The brains of many Hawaiians were studied in the late 1990s and early 2000s, and those that had a high level of milk consumption had residues of pesticides that had deposited in the brain tissue.

There was evidence of a reduced number of brain cells in those with the higher consumption of milk, and this was attributed to the greater exposure to pesticides. The reduced number of brain cells was considered to be a risk factor for Parkinson's disease — one of the causes of Parkinson's disease is thought to be excessive exposure to pesticides.

With the rise of recreational and medicinal marijuana across the U.S., pesticides have become a growing concern. Currently, there are no standards governing the use of pesticides in the growing and processing of marijuana. Ingesting a pesticide can be damaging, as demonstrated by the experiences with milk. Inhaling pesticides can also harm brain tissue.

One study found that 70 percent of the marijuana tested had toxins such as pesticides. For a medical marijuana user who is already neurologically impaired, this can be devastating.

Seven states specifically approve of marijuana use for Parkinson's disease. Dr. Ethan Russo, a internationally recognized clinician scientist with decades of experience with cannabis, recently published an overview of medical cannabis. He voiced concerns over the toxins in marijuana.

"New and disturbing data on pesticide residues in legal cannabis products in Washington state are presented with the observation of an 84.6 percent contamination rate including potentially neurotoxic and carcinogenic agents," Russo said.

The Oregon Health Authority recently issued warnings to consumers about products with high levels of pesticide and estimated that at least 130 people were impacted. A California based cannabis testing lab, Steep Hill, also reported that 84 percent of the medical marijuana samples they tested contained a high percentage of pesticides.

"Those in the cannabis community who feel that all cannabis is safe are not correct given this data. Smoking a joint of pesticide-contaminated cannabis could potentially expose the body to lethal chemicals," says Jmichaele Keller, president and CEO of Steep Hill. "As a community, we need to address this issue immediately and not wait until 2018."

Russo expressed concern and alarm regarding the potential harm to medical marijuana users.

"The unregulated commerce in cannabis with respect to pesticide usage and lack of available organic certification have resulted in widespread abuse of the legal cannabis market system," he said. "These products present a clear and present danger, particularly to young patients with epilepsy and other neurological conditions."

Young and old are at risk from pesticides. We learned this from milk years ago. Sadly, we are learning this from marijuana now.