It’s common knowledge that zinc can help fight cold symptoms, but it may not always work for you. Dr. Michael Smith, M.D., dubbed “the country doctor with a city education” and host of Healthy Talk radio, believes it comes down to three essential things: timing, type, and dose.

Zinc’s Cold Fighting History

Zinc was recognized for its powerful immune system benefits around the 1970s, when it was used alongside chemotherapy in patients with cancer. Radiation from chemotherapy can knock out production of white blood cells in your body, lowering your immune defenses. Zinc helps activate plasma cells that produce antibodies, thereby countering the effects of chemotherapy on your immune system.

Dr. Smith tells of a young girl that prompted the medical world to take a closer look at the relationship between zinc and colds. This young girl was around three years old and was being treated for leukemia. She ended up developing a severe cold and couldn’t take her zinc pill anymore, so the nurses simply let it dissolve in her mouth. The small 50 mg zinc tablet completely dissolved, and within hours the severe cold symptoms began to disappear. It’s here that the “zinc is good for colds” market began.

In 1994, the first double-blind human study on zinc lozenges was performed, and results showed that cold symptoms vanished after just seven days in 86 percent of people taking zinc compared to just 46 percent that took a placebo. Just last year the Journal of American Medical Association published a summary of human trials using zinc lozenges. The results again showed that properly using zinc within 24 hours of the first symptoms cut the duration of the cold by about 50 percent. According to Dr. Smith, the “proper use” part is what really makes a difference in how effective zinc will be.

Timing, Type, and Dosage

One variable for zinc’s effectiveness is timing, believes Dr. Smith. When it comes to taking zinc for fighting a cold, you need to take it immediately. Timing is absolutely critical, and not taking it as soon as the first symptoms show up could mean less chance of improvement. Doctors may find that prescribing zinc to sick patients doesn’t really work, but that’s because most people usually wait until the cold is becoming too bothersome. It’s usually at least a few days before a doctor gets to see a patient suffering from a cold, and by then, it’s too late for the zinc to work properly.

The type of lozenge you take also plays a role in how well zinc fights off your cold. Most lozenges used to be made with zinc oxide, but the zinc held onto the oxide too much and very little actually came off. If you don’t get an ample amount of zinc, there won’t be enough to coat cells and block the cold virus from entering into the cell, so this method wasn’t working as well as it could have been. Today, most lozenges are zinc acetate, which is more effective and release almost 100 percent of zinc into your body.

Lastly, Dr. Smith’s studies and reviews have led him to believe that having the right dosage will make a huge difference. If you begin taking zinc acetate as soon as symptoms begin to develop, 18.75mg between two to three times each day for several days will do the trick.