"We were struck by the fact that it didn't matter whether it was a diet or regular soda that participants consumed, the association with increased risk was present," said Ramachandran Vasan, M.D., senior author of the Framingham Heart Study and professor of medicine at Boston University School of Medicine. "In those who drink one or more soft drinks daily, there was an association of an increased risk of developing the metabolic syndrome.metabolic syndrome is a cluster of cardiovascular disease and diabetes risk factors including excess waist circumference, high blood pressure, elevated triglycerides, low levels of high-density lipoprotein (HDL good cholesterol) and high fasting glucose levels. The presence of three or more of the factors increases a person's risk of developing diabetes and cardiovascular disease.

Prior studies linked soft drink consumption to multiple risk factors for heart disease. However, this study showed that association not only included drinking regular calorie-laden soft drinks, but artificially sweetened diet sodas as well, researchers said.

"Moderation in anything is the key," said Ravi Dhingra, M.D., lead author of the study and an instructor in medicine at Harvard Medical School. "If you are drinking one or more soft drinks a day, you may be increasing your risk of developing metabolic risk factors for heart disease."

The Framingham study included nearly 9,000 person observations made in middle-aged men and women over four years at three different times.

In a 'snapshot in time' at baseline, the researchers found that individuals consuming one or more soft drinks a day had a 48 percent increased prevalence of the metabolic syndrome compared to those consuming less than one soft drink daily.

In a longitudinal study of participants who were free of metabolic syndrome at baseline (6,039 person observations), consumption of one or more soft drinks a day was associated with a 44 percent higher risk of developing new-onset metabolic syndrome during a follow-up period of four years.

The researchers also observed that compared to participants who drank less than one soft drink daily, those who drank one or more soft drinks a day had a: 31 percent greater risk of developing new-onset obesity (defined as a body mass index [BMI] of 30 kilograms/meter2 or more); 30 percent increased risk of developing increased waist circumference; 25 percent increased risk of developing high blood triglycerides or high fasting blood glucose; 32 percent higher risk of having low HDL levels. A trend towards an increased risk of developing high blood pressure that was not statistically significant.

Researchers then analyzed a smaller sample of participants on whom data on regular and diet soft drink consumption was available from food frequency questionnaires. Participants who consumed one or more drinks of diet or regular soda per day had a 50 to 60 percent increased risk for developing new-onset metabolic syndrome, said Dhingra, who is also an attending physician at Alice Peck Day Memorial Hospital in New Hampshire. "It didn't matter whether it was a diet or regular soft drink."

"Results also don't appear to be driven by the dietary pattern of soft drink users, i.e, by other food items that are typically consumed along with soft drinks," Vasan said. "We adjusted in our analyses for saturated fat and trans fat intake, dietary fiber consumption, total caloric intake, smoking and physical activity, and still observed a significant association of soft drink consumption and risk of developing the metabolic syndrome and multiple metabolic risk factors."

One explanation is that the fructose corn syrup in regular soft drinks causes weight gain, and can lead to insulin resistance and diabetes, Vasan said. "But then you would expect to see an association with regular soft drinks, but not diet soft drinks. Our findings suggest that this is not the case." Another possible explanation is that consuming more liquids is associated with a lesser degree of dietary compensation. Usually if you eat a large meal, then you're inclined to eat a smaller amount at the next meal, Vasan said. But liquids don't have the same degree of compensation as solids. If you drink a large amount of liquids at a meal, you are more likely to eat a larger amount at the next meal (compared to what you would eat had you consumed more solids at the prior meal).

Other theories are that the high sweetness of diet and regular soft drinks makes a person more prone to eat sweet items, or the caramel content in soft drinks may promote development of advanced glycation end products, complexes of sugars that can result in insulin resistance and can cause inflammation in experimental studies.

"These are all theories, and experts debate their importance," Dhingra said. "Our study was observational, and so right now all we demonstrate is an association. We have not proven causality."

Dhingra and Vasan called for further studies to replicate the results and to understand the mechanisms driving this association before recommendations can be made.

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2. For what health purposes are colloidal silver products marketed?

Colloidal silver products are often marketed with various unproven health-related claims. Examples include that they benefit the immune system; kill disease-causing agents such as bacteria, viruses, and fungi; are an alternative to prescription antibiotics; or treat diseases such as cancer, HIV/AIDS, tuberculosis, syphilis, scarlet fever, shingles, herpes, pneumonia, and prostatitis (inflammation of the prostate).

3. Do colloidal silver products work?

Reviews in the scientific literature on colloidal silver products have concluded that2-5:

Silver has no known function in the body. Silver is not an essential mineral supplement or a cure-all and should not be promoted as such. Claims that there can be a "deficiency" of silver in the body and that such a deficiency can lead to disease are unfounded. Claims made about the effectiveness of colloidal silver products for numerous diseases are unsupported scientifically. Colloidal silver products can have serious side effects (discussed further below). Laboratory analysis has shown that the amounts of silver in supplements vary greatly, which can pose risks to the consumer.

4. What are the risks of using these products?

Animal studies have shown that silver builds up in the tissues of the body. In humans, buildup of silver from colloidal silver can lead to a side effect called argyria. It causes a bluish-gray discoloration of the skin, other organs, deep tissues, nails, and gums. Argyria cannot be treated or reversed, and it is permanent. While it is not known how argyria occurs, it is thought that silver combines with protein, forming complexes that deposit in the skin and are processed by sunlight (as in traditional photography).6,7 Other side effects from using colloidal silver products may include neurologic problems (such as seizures), kidney damage, stomach distress, headaches, fatigue, and skin irritation. Colloidal silver may interfere with the body's absorption of the following drugs: penacillamine, quinolones, tetracyclines, and thyroxine.5

5. Does the Government regulate dietary supplements containing colloidal silver?

Yes, the Government regulates them, but differently than drugs. The Dietary Supplement Health and Education Act of 1994 places dietary supplements in a special category of foods. This category is regulated differently than other foods and than drugs. For example, manufacturers of dietary supplements, unlike manufacturers of drugs, do not have to prove their product's safety and effectiveness to the FDA before it is marketed. If the product is found to be unsafe after it is marketed, the FDA can take certain actions, such as removing it from the marketplace. The FDA issued a ruling in 1999 that no products containing colloidal silver are generally recognized as safe and effective. The FDA and the Federal Trade Commission (FTC) have sent warning letters to the operators of many Web sites that market colloidal silver with drug-like claims (i.e., that their product diagnoses, treats, cures, or prevents disease).

6. What should people do who are considering or using colloidal silver?

Tell your health care providers about any complementary and alternative practices you use. Give them a full picture of what you do to manage your health. This will help ensure coordinated and safe care. This is especially important if you are pregnant, nursing a baby, or considering treating a child.

References

Agency for Toxic Substances and Disease Registry. ToxFAQs for Silver. Agency for Toxic Substances and Disease Registry Web site. Accessed at atsdr.cdc/tfacts146.html on December 11, 2006 Fung MC, Bowen DL. Silver products for medical indications: risk-benefit assessment. Journal of Toxicology. Clinical Toxicology. 1996;34(1):119-126. Gulbranson SH, Hud JA, Hansen RC. Argyria following the use of dietary supplements containing colloidal silver protein. Cutis. 2000;66(5):373-374. FDA bans colloidal silver products, cites lack of data. FDA Consumer. 1999;33(6). Accessed at fda/fdac/departs/1999/699_upd.html December 11, 2006. Natural Medicines Comprehensive Database. Colloidal silver. Natural Medicines Comprehensive Database Web site. Accessed on December 11, 2006. White JM, Powell AM, Brady K, et al. Severe generalized argyria secondary to ingestion of colloidal silver protein. Clinical and Experimental Dermatology. 2003;28(3):254-256. Hori K, Martin TG, Rainey P, et al. Believe it or not--silver still poisons! Veterinary and Human Toxicology. 2002;44(5):291-292.