Finding the best in nutritional supplements means you have to watch for a number of important factors. All of these things can effect the quality of your supplement.
Tablets or Vegetable Capsules
The ingredients in a tablet undergo a great deal of pressure and heat. Enough to lower the nutrient levels by 25%, and can even create unexpected byproducts within the tablet. Tablets are also absorbed by the body 50% less effectively than vegetable capsules.
Synthetic Vitamins and Minerals
Vitamins and minerals that are created in a lab are not healthy. Simple as that. They can cause damage on a cellular level because they are not compatible with our bodies. Any benefits from synthetic ingredients are short-lived and their toxins will eventually have to be cleansed from your body.
Isolated Vitamins or Minerals
Natural vitamins and minerals naturally exist as complexes with other substances, not as individual molecules. To get the full benefit of their healthful properties, they should be taken in the same way. Supplements with single vitamins or minerals are not as well utilized by the body.
Herbs grown in the USA are contaminated by fumigation and irradiation procedures, effecting more than half the material harvested for nutritional purposes. This can even be the case with herbs labeled "organic". Non-organic plants can also be treated with a mix of pesticides and insecticides.
Growing and Harvesting
During the growing period, a plant can vary in mineral and vitamin content by as much as 900%. So herbs used in supplements must be harvested at the absolute peak of maturity for the most benefit.
Tablet supplements can be made with a range of glues, fillers, binders, and lubricants. None of these substances are healthy, and may even be toxic to your body. Talcum powder is used in tablet making, and may be a carcinogen. You won't find this information on any product label.
The risk of being exposed to infectious prions exists when any animal-organ or glandular products are used in supplement ingredients. Another possible risk is animal-derived digestive enzyme, which also have toxic residue from antibiotics, pharmaceuticals or synthetic hormones used in typical animal husbandry.
Vegetable or Gelatin Capsules
Vegetable capsules are much easier to digest because they dissolve so quickly. Their fiber content also helps with nutrient uptake. With vegetable capsules, you have to make sure they are 100% free of preservatives and made with non-toxic ingredients. Gelatin capsules can have 1 to 2% toxic preservatives or even carry infectious prions (the molecules that can cause "mad cow disease").
Other Factors to Avoid with Supplements
Some other ingredients you really should avoid: soy, wheat, sugar, salt, corn, magnesium stearate and other artificial colors and preservatives. Not all of these are hazardous when in their natural states (like soy), but they can be genetically altered or be treated with chemicals before harvest. As for things like "natural flavor", MSG is often used and is not healthy for your body.
If you really want to find the best and most healthful supplements, find companies that have full disclosure about their products. They should tell you where all the raw materials have come from, as well as their manufacturing and packaging procedures.