Vitamins and Minerals: What you need to know by Harvard Medical School

Vitamins and Minerals: What you need to know by Harvard Medical School

Understanding how vitamins and minerals interact in our body gives us a valuable means of taking our health into our own hands. Research into the effects of these micronutrients has been enlightening.

For example, we now know that a large fraction of Americans are not getting enough vitamin D, and the range of consequences may be far greater than we thought.
Recent studies suggest that vitamin D does more than help build strong bones; it may help to prevent hypertension, certain types of cancer, and some autoimmune diseases. We also believe, with an increasing degree of certainty, that getting enough folic acid can counteract some of the adverse effects of consuming alcohol.
Researchers are constantly making such discoveries, and often their findings have far-reaching effects. But it’s worth keeping in mind that while nutrition research can yield powerful answers, it also raises new questions.

Nutrition is endlessly complex, and the research is invariably in a state of flux. Not only do nutrients interact with one another (making it difficult to isolate their effects) but they also interact with genes, drugs, and even lifestyle factors. For some nutrients, such as selenium, there’s a narrow range between too little and too much, and that amount varies from person to person This Special Health Report provides the latest evidence and mineral and vitamin information so that you can make healthy choices about what foods to eat and what supplements to take.
Because nutritional science continues to evolve, this report also contains tips on how to judge new studies on vitamin benefits and put the findings in context. Prepared by the editors at Harvard Health Publications in consultation with Meir J. Stampfer, M.D., Dr.P.H., Professor of Epidemiology and Nutrition, Harvard School of Public Health. 45 pages. (2008)
1. Vitamins and minerals: The basics
• Water-soluble vitamins
• Fat-soluble vitamins
• Major minerals
• Trace minerals
2. Your diet: Building a solid foundation
• Eating well
• Getting the most from foods
3. Making sense of scientific studies
4. Federal guidelines
5. Cast of characters: Key vitamins and minerals
• Vitamin A and carotenoids
• B vitamins
• Vitamin C
• Vitamin D
• Vitamin E
• Vitamin K
• Calcium
• Magnesium
• Potassium
• Selenium
6. SPECIAL BONUS SECTION: The virtues of vitamin D
7. Vitamins, minerals, and your health
• Your heart and blood vessels
• Your cancer risk
• Your mind and memory
• Your bones
• Your eye
8. Supplements: Filling in dietary gaps
• Potential pitfalls
• More isn’t always better
• Specialized supplements for women, men, and older adults
• Advice on choosing a supplement
9. Beyond vitamins: Fish oils and promising phytochemicals
• Fish oils and your heart
• Phytochemicals
10. Getting too little
• Are you deficient?
11. Getting too much
• Avoiding overload
12. Resources
13. Glossary
What’s special about vitamin D? This fat-soluble vitamin is exceptional among vitamins in three ways. First, it has a unique mechanism of action in the body. Second, you can’t get very much of it naturally through your diet. And third, many Americans are deficient in this vital nutrient. That final point is keenly important, in light of burgeoning evidence that vitamin D’s health benefits extend far beyond its reputation for building healthy bones. Over the past decade, studies suggest that adequate amounts of vitamin D may lessen the risk of several types of cancer (including cancers of the colon, prostate, and breast) and may also play a role in preventing high blood pressure, multiple sclerosis, and even schizophrenia. And a 2007 meta-analysis of 18 randomized controlled trials showed that vitamin D supplementation may even help people to live longer.
How D is different
Unlike other vitamins, which are antioxidants or key players in enzyme reactions in the body, vitamin D functions in the body as a hormone—that is, a substance made by one organ that sends a chemical message to another organ to elicit a specific response. One of vitamin D’s best-known and important roles is to signal the intestines to absorb calcium into the bloodstream. Without sufficient vitamin D, your body will break down bone to get the calcium it needs—no matter how much calcium you consume through food and supplements. Vitamin D is also unusual be- cause it’s relatively scarce in normal diets. To get just 400 international units (IU) of vitamin D (the current recommended daily amount for people ages 50–71), you’d need to eat about 5 ounces of salmon, 7 ounces of halibut, 30 ounces of cod, or a 6-ounce can of tuna, or drink four cups of milk. Few people include that much fish—or milk, for that matter— in their daily fare. Milk actually doesn’t normally contain vitamin D, but nearly all the milk sold in the United States today is vitamin- D fortified. This practice began in the 1930s to combat rickets, a disease that leads to soft, weak bones caused by vitamin D deficiency. It’s worth noting that dairy products made from milk, such as cheese, yogurt, and ice cream, aren’t typically fortified with vitamin D and contain only small amounts.
In fact, casual exposure to sunlight provides people with most of their vitamin D requirement (see Figure 5). Sunlight contains two forms of radiant energy, ultraviolet A (UVA) and ultraviolet B (UVB). UVB provides the energy your body needs to generate vitamin D, which is why it’s known as the “sunshine vitamin.” If you sit outside on a sunny day in the middle of summer at the equator wearing only a swimsuit, your body creates a whopping 20,000 IU of vitamin D per hour. But even people who don’t sunbathe or spend a great deal of time outside probably generate a fair amount just walking outside for short periods throughout the day, depending on the latitude and the amount of skin that is exposed. However, a number of factors—including the season, time of day, and where you live—can affect how much UVB reaches your skin. What’s more, your age, skin color, and sunscreen use also influence your skin’s production of vitamin D. A confluence of these factors can conspire to limit vitamin D levels, which is why a surprisingly large number of Americans—more than 50% among certain groups—are deficient in vitamin D.