The Linus Pauling Institute
Micronutrient Information Center

Jane Higdon, Ph.D., R.N.
Linus Pauling Institute
Research Associate

Anyone can be easily overwhelmed by the amount of seemingly contradictory information about nutrition and health publicized daily. The shelves of nutritional and herbal supplements are constantly expanding in our supermarkets and drug stores, displaying impressive claims that imply effective treatment for any number of conditions. The World Wide Web contains countless websites devoted to nutrition and health. Although some of them contain useful and accurate information, others use unsubstantiated claims to promote a variety of products.

The Linus Pauling Institute is committed to advancing the understanding of the role of nutritional factors in health and disease through research and education. Consequently, we are pleased to introduce our Micronutrient Information Center, a website designed to provide up-to-date, scientifically accurate information on micronutrients (vitamins, minerals, and other nutrients) and phytochemicals (plant chemicals that may affect health) and their roles in health and disease. The Linus Pauling Institute does not endorse any particular nutritional supplement product and has no financial interest in promoting the use of any micronutrient or phytochemical discussed in the Micronutrient Information Center.

What Research is Emphasized

Human research published in peer-reviewed journals has been emphasized whenever possible in the Micronutrient Information Center. In peer-reviewed journals, scholars in the same field or specialty as the investigators critically review a draft of the article prior to its publication. When relevant, other types of research are presented, such as research performed using cell culture or animal models.

A number of different research designs have been applied to nutritional studies in humans, each with its own limitations with respect to validity and relevance. Most studies can be defined as either observational or experimental. For example, in the investigation of the effect of nutrient intake on a disease outcome, participants would be assigned to different nutrient intake groups by the investigator in an experimental study, while the investigator would have no control over a participant's nutrient intake level in an observational study. In an observational study, other factors might influence the nutrient intake of a participant and also the disease outcome, potentially affecting the validity of the results. In general, experimental studies provide the strongest evidence for the effect of nutrient intake on a disease outcome. However, it is not always ethical or practical to perform an experimental investigation.

Several characteristics add to the credibility of experimental studies and are frequently referred to in the Micronutrient Information Center.

  • Randomized selection of participants into different groups (e.g. treatment and control) is important in eliminating bias that might arise from self-selection or selection by the investigator.
  • Placebo-controlled studies provide an inactive treatment or "placebo" to a control group while the experimental group receives the treatment(s) of interest to ensure that significant effects are due to the experimental treatment.
  • In a double-blind study neither the participants nor the investigators administering the treatment know which participants are receiving the treatment(s) or the placebo, eliminating the possibility of bias on the part of the investigators or the participants.

Several types of observational studies have been utilized to obtain useful information about nutrient intake and disease.

  • Cross-sectional studies measure nutrient intake and disease outcome at the same point in time in a study population. With cross-sectional studies it cannot be determined whether the level of nutrient intake preceded or followed the disease outcome.
  • Retrospective studies measure the disease outcome in the present, while nutrient intake in the past must be assessed in some manner, usually by recall using questionnaires. While retrospective studies provide information about nutrient intake before the disease outcome of interest occurred, it is often difficult to get reliable assessments of past nutrient intake.
  • Prospective studies (also called cohort or longitudinal studies) measure nutrient intake in the present in healthy individuals while disease outcome is determined in the future. Among observational studies, prospective studies have the advantage of providing accurate information regarding nutrient intake and disease outcome, in addition to ascertaining that the intake of the nutrient preceded the disease outcome.
  • Case-control studies start by identifying a population with the disease outcome of interest and then identify a reference (control) group that does not have the disease outcome of interest. Obtaining an appropriate control group is sometimes difficult in case-control studies. Case-control studies may be either cross-sectional or retrospective. 

Increasingly, policy or treatment decisions are based on the results of systematic reviews and meta-analyses. In a systematic review, investigators compile all available scientific literature relating to the research question and rate the scientific quality of the studies prior to drawing a conclusion. A mathematical or statistical analysis used to pool all of the results and provide an overall estimate of the effect is known as a meta-analysis. When available, the results of systematic reviews and meta-analyses are presented in the Micronutrient Information Center.

Types of Nutrient Intake Recommendations

In the United States, the Food and Nutrition Board of the Institute of Medicine appoints committees of scientists to set the Dietary Reference Intakes (DRIs), which are used to plan and evaluate diets of apparently healthy people (see the article "The New Recommendations for Dietary Antioxidants" in the Spring/Summer 2000 LPI newsletter). Three different DRIs may appear in the Micronutrient Information Center.

  • The Recommended Dietary Allowance (RDA) is the dietary intake level of a specific nutrient sufficient to meet the requirement of nearly all (97%-98%) healthy individuals in a particular life stage group.
  • The Adequate Intake (AI) is the recommended intake level of a specific nutrient assumed to be adequate. It is used when an RDA cannot be determined.
  • The Tolerable Upper Intake Level (UL) is the highest level of a nutrient determined to pose no risk of adverse effects for almost all individuals in the general population.

The RDA and the AI are usually set at a level aimed to avoid deficiency of a given nutrient that might lead to a deficiency disease. Therefore, the RDA or the AI for a particular nutrient is addressed in the "Deficiency" section of the Micronutrient Information Center, while the UL is addressed in the "Safety" section.

Nutrient recommendations from the Linus Pauling Institute are based on relevant scientific research and aimed at prevention of chronic disease and promotion of optimal health. "The Linus Pauling Institute Recommendation" is presented in its own section for each nutrient addressed by the Micronutrient Information Center.

Neither the DRIs nor the Linus Pauling Institute recommendations address the treatment of disease. Physiologic and, more commonly, pharmacologic doses of nutrients have been investigated as treatments for a number of chronic diseases. A physiologic dose refers to the intake level of a nutrient associated with the prevention of deficiency or the maintenance of health and is not generally greater than that which could be achieved through a proper diet. A pharmacologic dose is generally associated with the treatment of a disease state and considered to be a dose at least 10 times greater than that needed to prevent deficiency. In general, the considerations of risk and benefit of treatment with pharmacologic doses of a nutrient are different when considering treatment of a disease rather than disease prevention in a generally healthy individual. When well controlled research is available, the treatment of disease with pharmacologic doses of specific nutrients is reviewed in the "Disease Treatment" section.

Navigating the Micronutrient Information Center: An Introduction to the World Wide Web

The Internet is a large collection of computers all over the world that store and share information. The World Wide Web consists of millions of individual web pages that are linked to other pages. A unified collection of related pages is known as a website. Each website has a home page, which is like an entry way or a table of contents.

To access the Internet one needs a computer equipped with software called a web browser (Netscape and Internet Explorer are the most popular), an Internet Service Provider (ISP) or online service, and a means of connecting to the Internet by telephone modem or special cable. Those who don't have computers or Internet connections at home will often find them accessible at their community library or a nearby university library, along with librarians knowledgeable about their use.

Once connected to the Internet, the web browser can be used to view web pages. All websites have addresses called URLs (Uniform Resource Locator). The Linus Pauling Institute's URL is On October 15, 2000, a link to the Micronutrient Information Center will appear on the Linus Pauling Institute Home Page.

The LPI Micronutrient Information Center Home Page

Blue buttons on the displayed home page allow for navigation of the site. For instance, clicking on the "Vitamins" button will provide a link to an introductory page on vitamins, which includes links to information on each of the 14 individual vitamins. The minerals, phytochemicals, and a category we call "other nutrients" will be handled in the same way. As of October 15 only the vitamins will be available. However, minerals, phytochemicals, and other nutrients will follow.

The Contents section provides an expanded table of contents with a list of each individual nutrient or phytochemical that is currently available on the site, as well as a list of diseases and health issues. Clicking on the nutrient provides an immediate link to the web page covering that particular information.

A search engine is also available on the Micronutrient Information Center Home Page. It can be used to search the site for a specific topic, such as "atherosclerosis" or "folic acid". The search engine will generate a list of web pages from the Micronutrient Information Center that contain pertinent information.

Individual Nutrient Web Pages

Each individual nutrient page can be read in its entirety by scrolling down the document, or it can be read in sections. In general, each nutrient page includes sections on function, deficiency, disease prevention, disease treatment, LPI recommendation, food sources, safety, recent research, and references. Any words that are highlighted with a different color and are underlined are linked to the Glossary, where definitions are provided. Colored and underlined phrases in boldface are linked to relevant LPI Newsletter articles or news releases. References are numbered so clicking on a number in parentheses takes the reader to the associated reference in the scientific literature located at the end of the page.

The entire text of a nutrient page may be printed if your computer is connected to a printer. Most of the text portions will be 7 to 9 pages long.

Future Developments

Individual minerals, phytochemicals, and other nutrients will be added to the website over the coming year. Check the "Overview" section periodically to see which nutrients have been added. One of the advantages of the World Wide Web is the ease with which information can be updated. When interesting new research is published, the "Recent Research" sections for individual nutrients will be updated. We want the Linus Pauling Institute Micronutrient Information Center to be an accessible and responsive resource for exploring the complex interrelationships between nutritional factors and health as they emerge.

Printed copies of the information in the Micronutrient Information Center will be available for a small fee. Please note, however, that printed information will be updated much less frequently than the information on the website.

Last updated November, 2000

Honoring a Scientific Giant with Nutritional Research Toward Longer, Better Lives

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