Benefits and risks of 5 most common supplements

By Naveed Saleh, MD, MS, for MDLinx
Published December 11, 2019

Key Takeaways

According to a report commissioned by the Council for Responsible Nutrition (CRN), the leading trade association for the supplement biz, dietary supplements contributed approximately $122 billion to the US economy in 2016 alone, and experts have projected increased and sustained growth in the supplements industry in the foreseeable future. 

“The dietary supplement industry is a robust industry, and this new economic analysis further demonstrates the important and positive impact our industry has on people’s lives,” Steve Mister, Esq, CAE, president and CEO of CRN, told

Driving much of this growth is the surge in consumer demand for health and wellness products, according to key findings from the report. And although it’s encouraging that so many Americans are focused on improving their health and well-being, it’s important to note that a significant proportion does not have nutritional deficiencies requiring the use of supplements. While it’s true that most supplements can provide some health benefits, these positive effects may be negated by excess consumption or incorrect usage.

Here are five of the most commonly used dietary supplements whose full health effects you should be aware of before taking them.


Zinc plays a role in a gamut of homeostatic, catalytic, and molecular functions. As such, it is found in many proteins, particularly fish, meat, legumes, and whole grains.

Although zinc deficiency is rare, zinc is a popular supplement sold for common cold treatment, cancer prevention, diabetes treatment, infertility treatment, wart treatment, and so forth. However, there have been mixed study results regarding any benefit of zinc in terms of acute respiratory infections, immunity, and diabetes, among both children and adults.

When taken within 24 hours of symptom onset, zinc could decrease the duration of a cold, according to some researchers. Not surprisingly, zinc is commonly placed in lozenges to decrease the binding of viruses to the oropharynx. Large amounts of zinc, however, can lead to decreased immunity, chills, headache, fatigue, and fever.

Of note, when zinc is taken with iron, intestinal absorption of both elements is lowered. Zinc decreases the bioavailability of fluoroquinolones and tetracyclines.


Nicotinamide is formed in the body from food precursors rich in niacin, such as poultry, fish, legumes, nuts, and cereal grains. It is a water-soluble form of niacin (ie, vitamin B3). Researchers have suggested that nicotinamide may decrease the risk of some skin lesions and non-melanoma skin cancers in those with sun-damaged skin, but unfortunately not in renal transplant recipients.

In the clinic, nicotinamide is used to treat inflammatory skin conditions such as acne vulgaris and rosacea. It is also used to treat pellagra, or niacin deficiency. As a supplement, nicotinamide is sold to prevent skin cancer.

Nicotinamide has been shown to improve the repair of UV radiation-induced DNA damage in melanocytes and keratinocytes. In clinical trials, nicotinamide decreased UV- and photodynamic therapy-induced immunosuppression.

Nicotinamide is relatively well-tolerated at low doses. At higher doses, however, it can cause gastrointestinal disturbance, headache, and so forth.


Beta-carotene (ie, vitamin E) is an antioxidant sold for eye disorders, cancer prevention, HIV/AIDS treatment, immunostimulation, heart disease, and oral leukoplakia (ie, white patch or plaque). Evidence on the health effects of beta-carotene, however, are mixed, with unclear effects on heart disease, cancer, and CD4 counts. Notably, the US Preventive Services Task Force (USPSTF) came out against beta-carotene or vitamin E supplements for the primary prevention of heart disease or cancer.

Apricots, papaya, cantaloupe, and other orange or yellow fruits are rich sources of beta-carotene. In some studies, beta-carotene induced apoptosis and decreased cell growth in cancer cell lines via caveolin-1 expression.

When taken with alcohol, beta-carotene can potentiate liver damage. Moreover, alcohol negatively offsets any potential chemopreventive effects of beta-carotene. Befittingly, when taken chronically, beta-carotene can result in carotenodermia, or a harmless yellowing of the skin.


Turmeric is a rhizome endemic to South Asia and is used as a spice and coloring additive in traditional dishes. In folk medicine, it is used to treat indigestion, inflammation, and constipation. As a dietary supplement, turmeric is marketed to help with cognition, cancer prevention, and arthritis.

Turmeric is relatively well tolerated, with gastrointestinal discomfort being a possible adverse effect. It exhibits drug-herb interactions with various types of chemotherapy, pain relievers, and anticoagulants.

The active ingredients in turmeric are turmerone oil and water-soluble curcuminoids, with the curcuminoid curcumin best researched. Curcumin is a weak phytoestrogen with choleretic, anti-inflammatory, antiproliferative, immunomodulatory, and chemopreventive effects. Curcumin has also been found to be beneficial in the treatment of mood disorders and irritable bowel syndrome.

Curcumin is rapidly absorbed and metabolized. However, it has been shown to interfere with cytochrome P450 enzymes and chemotherapy drugs, including cyclophosphamide and doxorubicin. 


Biotin is a B vitamin found in eggs, meat, and vegetables. It is an essential coenzyme in carbohydrate and lipid metabolism. It initiates microtubule formation in neurons, with deficiency possibly causing neuropathy. Biotin could also decrease interleukin and interferon activities, as well as leukocyte numbers.

Biotin supplements are sold for cancer prevention, osteoporosis, multiple sclerosis, immune regulation, and seasonal affective disorder.

According to limited research, biotin may help with brittle nails. Furthermore, in preliminary studies, biotin was associated with improvement in multiple sclerosis, diabetic neuropathy, and—when combined with chromium—glycemic control in those with diabetes. It remains to be elucidated whether biotin helps with hair loss caused by chemotherapy.

Interestingly, biotin supplementation can interfere with results from various immunoassays, including hCG, thyroid, and troponin.

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