The U.S. Preventive Services Task Force does not recommend the routine use of vitamin or mineral pills to prevent chronic diseases (USPSTF Bulletin, May 4, 2021). Heart disease is the leading causes of death in the U.S. today, but taking vitamin pills has not been shown to prevent heart disease, and neither the American Heart Association nor the American College of Cardiology recommend them. A study of 14,000 middle-aged doctors found that those taking vitamin pills for more than 10 years did not have a reduced incidence of heart attacks, strokes, or death (JAMA, Nov 7, 2012;308(17):1751-60). Multivitamins also have not been shown to prevent dementia; an analysis of 28 different studies that followed more than 83,000 healthy people over age 40 for up to 18 years found that pills containing B vitamins, beta carotene, vitamins C, vitamin D, vitamin E, zinc, copper or selenium (alone or in combinations) did not prevent or treat dementia and loss of brain function with aging (Cochrane Database of Systematic Reviews, December 17, 2018).

All of the vitamins necessary for human life and health come from foods, with the exception of vitamin D which comes primarily from sunlight. Your body requires 13 vitamins and more than 15 minerals, but taking vitamin or mineral pills will not compensate for a poor diet, obesity, lack of exercise, smoke or alcohol. You should be preventing disease and prolonging life by eating a healthful, plant-based diet that limits sugar-added foods, mammal meat, processed meats and fried foods. Then check with your doctor to see if you need tests for specific deficiencies, particularly:
vitamin D in people who do not get sun exposure
vitamin B12 in older people and vegetarians
protein in people who eat no animal products

Your risk for B12 deficiency increases with age because you can lose much of your stomach acidity that is necessary to help you absorb B12. Most healthful diets restrict animal products, the major source of B12 (Annu Rev Nutr, 1999;19:357-77), and vegans and vegetarians may also suffer from other deficiencies (Nutr Rev, 2013 Feb;71(2):110-7).

How Vitamins Work in Your Body
Most vitamins, particularly the B vitamins, are parts of enzymes that start chemical reactions. Chemical reactions break down food so that it can be absorbed into your bloodstream, start the processes that turn food into the fuel that your body uses for its various functions, and build and repair all of the tissues in your body. All of these chemical reactions are started by enzymes made by your body and by the bacteria that live in your body.

For example, for chemical A to go to chemical B and release energy for your cells to use, you need a first enzyme to start that chemical reaction. Then you need a second enzyme to break down chemical B to form chemical C and release more energy. If you have the first enzyme, you make lots of chemical B. If you lack the second enzyme that breaks down chemical B, chemical B could accumulate in large amounts in your body and may be toxic and harm you.

Scientists do not know all of the chemical reactions started by vitamins, but they have worked out how some of the B vitamins help to make all of the proteins in your body. All human protein is made up of building blocks called amino acids. Nine amino acids cannot be made by the human body, so they are called essential amino acids. The other 13 can be made from the essential amino acids, so you don’t need to get them from your food; these are called the non-essential amino acids

You use enzymes from the B vitamins to make the non-essential amino acid cysteine from the essential amino acid, methionine. However, methionine must go through several chemical reactions that make homocysteine before it makes cysteine. Thus Methionine > Homocysteine > Cysteine. However, homocysteine is associated with increased risk for heart attacks, so if it accumulates in the body it may be harmful. Vitamin B6 (pyridoxine) converts homocysteine to methionine and vitamin B9 (folic acid), and/or B12 (cobalamin) converts homocysteine to cysteine. Vitamin B3 (niacin) converts cysteine back into homocysteine. The B vitamins depend on all of the other B vitamins and more to avoid the buildup of toxic chemicals in your body.

Who May Benefit from Specific Vitamin or Mineral Pills
Many years ago, scurvy was common in people who did not eat fruit as a source of vitamin C, and beriberi was common in people who lacked thiamine because they did not eat whole grains. Today diets are more varied and many processed foods are fortified, so these deficiency diseases are rarely seen, and then usually only in illness or severe deprivation. North Americans die far more often from diseases caused by excess food than from deficiencies.

Doctors may recommend specific vitamins or minerals in their treatment recommendations for patients such as:
• people with conditions that make it difficult to absorb and retain some nutrients
• people with diseases that cause body or muscle wasting
• pregnant women
• vegans who eat no animal products at all and need a source of vitamin B12
• some older people who do not eat properly or people with restricted eating patterns
• vitamin D for people who do not get adequate sunlight
• people who cannot metabolize B12
• possibly people with macular degeneration
• people with stomach problems who must take proton pump inhibitors
• possibly some people on metformin to treat diabetes

My Recommendations
There is no scientific evidence that vitamin or mineral pills prevent dementia, heart attacks or chronic diseases. Micronutrients in food are typically better absorbed by the body than those from pills, so I do not recommend taking vitamin pills, mineral pills or other supplements unless you and your doctor have identified a special need such as those listed above.  Since nobody knows all of the chemical reactions that go on in your body, I recommend that you follow what most scientists consider to be healthful lifestyle habits (including diet), and not depend on pills that have more questions than answers.
• get plenty of exercise
• eat lots of vegetables, fruits, and seeds (nuts, beans, whole grains)
• restrict sugar-added foods and drinks, red meat, processed meats and fried foods
• avoid being overweight
• avoid all forms of tobacco
• restrict or avoid alcohol
• avoid recreational drugs and unnecessary prescription drugs or over-the-counter products