Clinical trials can and have been done on a variety of vitamins and other supplements. Such trials are not inexpensive to conduct, but they do provide scientific evidence about the efficacy of the product in question. I take the AREDS-2 vitamin supplement daily to prevent age related macular degeneration, a disabling eye condition that can lead to deteriorating vision. The National Eye Institute sponsored a large clinical trial of the vitamin and anti-oxidant mixture ( https://nei.nih.gov/areds2 ) that contains Vitamin C, zinc, copper and a couple of plant-based compounds. The trials showed that this mixture helps prevent further deterioration of the retina and my yearly retina scans show that in my case there has been no change.
Alan,
I'm not disparaging the efficacy of vitamins and natural dietary supplements. I'm just highlighting the complexity of the issues. There's also a large range of natural products which have been used by traditional societies as medicines and spices, for many centuries, which are claimed to have health benefits without the adverse side-effects of synthetic drugs.
Sometimes a few modern studies at universities reveal very promising results for such products, then other studies fail to replicate the results, for reasons that are often not explained or delved into.
Quite often, the funds to do more research are not available if the product cannot be patented. I'm thinking here of natural products such as Ginseng, Turmeric, Saffron and that compound in grapes called Resveratrol, which is considered to be one of the benefits of red wine, and is claimed to prolong life. (Although red wine does not contain enough Resveratrol to be effective, unless one drinks hug quantities.
)
I chose the example of Vitamin C because there still seems to be a controversy about the benefits of dosages higher the recommended minimum requirement of around 75 mg per day. I suspect the reason for this lack of certainty is due to the great variability of human biology and the fact that that the presence or absence of so many other factors can influence the results during scientific trials. Everything tends to be related in some way or to some degree.
For example, the bioavailability of certain supplements often depends on the presence of other substances. Calcium supplements are apparently not as effective if the person is lacking in Vitamin D. Before this was known, I can imagine how varied the research results would have been when providing only calcium supplements to the people involved in the trials.
This reminds me a of FACE experiment I read about recently (Free Air CO2 Enrichment) whereby CO2 is wafted over plants in their natural environment to examine its effect on growth.
The results of this particular experiment showed no significant increase in growth, contrary to other experiments which did show a significant increase in growth. (One can imagine the alarmists jumping up and down with glee
).
However, later examination of the techniques used in the experiment revealed that the researchers had wafted CO2 over the plants
only during the daytime, in order to save money. They had assumed that CO2 is taken up by all plants only during times of sunlight when photosynthesis takes place. This is apparently not true.
"Crassulacean acid metabolism, or CAM, is a mechanism whereby plants typically take up and store carbon dioxide during the night and use it in photosynthetic carbon dioxide fixation during the day, when sunlight is available."