There are a dozen or more vitamins that play an essential role in a wide variety of our bodies' functions. Getting these from a healthy, balanced diet is theoretically possible. Many actually do. But it can be difficult, especially today when so many are on the go.

Supplements can help fill the gap. Unfortunately, there is a large amount of junk science, and much more that simply isn't known for sure one way or the other, with respect to any weight loss supplement or nutritional aid. It pays to be cautious. It's your health.

For example, Vitamin C is needed to make collagen, an important feature of many proteins that go to make blood vessels, tendons and more. It also plays a role in making norepinephrine, a key neurotransmitter. A large amount of research exists to show that Vitamin C helps reduce free radicals that can damage cells. This antioxidant role is a factor in reducing the odds of cancer and other diseases.

Children should get from 15-25 mg per day, while adolescents need 75 mg (males) or 65 mg (females). Adult males need about 125 mg daily, females 75 mg. Orange juice is an excellent source, since it contains 75 mg in only 6 ounces. A cup of strawberries has 82 mg. Even a medium tomato will have about 23 mg. It's hard to 'overdose' on Vitamin C since any excess is excreted out in the urine.

The role of Vitamin A in vision has been well publicized. Every child knows he is 'supposed to eat his carrots'. But it also plays a part in maintaining the lining of the lungs, as well as that of the urinary and digestive tracts.

Adults need about 2300 IU (females) and 3000 IU (men). Good sources include carrots, of course. But a medium egg will supply about 280 IU. An ounce of Cheddar cheese has about 300 IU. Breakfast cereals may contain anywhere from 500-1000 IU.

But, unlike Vitamin C, it is possible to consume too much Vitamin A. A safe upper limit ranges between 8000-10,000 IU daily. Too much over a long period can produce vomiting or even liver damage. Still, many large surveys point to the conclusion that about 25% of adult Americans don't get enough in their diet.

There are a number of other essential daily vitamins, including members of the B-complex, D, E and others. But these two examples alone are enough to show that it requires some care to get the right amounts. Whether attempting to get all the needed vitamins from diet alone or by taking supplements, it's important to keep track of the amounts.

Those taking supplements as part of a weight loss program should find this easy. They're already tuned to monitoring their intake. But the same advice applies to anyone seeking to optimize their nutrition.