Nutritional Medicine: What It Is and Where the Evidence Stands

Nutritional medicine sits at an uneasy boundary. On one side are some of the most decisive successes in public health, such as the near elimination of scurvy, rickets and goitre in many countries. On the other are high dose nutrient protocols promoted with great confidence and little evidence. Practitioners who use nutrients therapeutically need to know both histories well, because patients and colleagues will judge the field by whichever side they encounter.

Defining the field

Nutritional medicine is broadly the use of diet and individual nutrients as therapy, as distinct from general dietary advice. It overlaps with clinical nutrition, which is usually delivered by dietitians and focuses on diet in disease, and extends to the therapeutic use of specific vitamins, minerals, fatty acids, amino acids and other nutrients, sometimes at doses well above those found in food.

A strand of the field, historically called orthomolecular medicine, proposed in the 1960s that high doses of nutrients could treat a wide range of conditions, from schizophrenia to cancer. The idea attracted considerable attention, partly because of its association with the Nobel laureate Linus Pauling, but its central claims were not supported by subsequent trials. Contemporary nutritional medicine has largely moved towards a more evidence based position, but echoes of the older approach remain in some practice.

The unambiguous successes

Several nutrient interventions are among the most robustly supported in medicine.

• Correcting deficiency. Iron for iron deficiency, vitamin B12 for pernicious anaemia and other deficiency states, iodine for iodine deficiency, vitamin D and calcium in deficiency, and thiamine in alcohol related deficiency and malnutrition.
• Folic acid and neural tube defects. A landmark randomised trial published in 1991 showed that folic acid taken before conception and in early pregnancy substantially reduced the recurrence of neural tube defects. Folic acid supplementation before conception, and food fortification in many countries, followed.
• Vitamin A in child health. In populations where deficiency is common, vitamin A supplementation reduces child mortality.
• Zinc in childhood diarrhoea. Zinc reduces the duration and severity of diarrhoea in children in low income settings.
• Specific metabolic disorders. Many inherited metabolic conditions are managed with precise dietary and nutrient therapy.

Supported uses beyond deficiency

Some nutrient therapies have evidence in specific conditions even without classical deficiency.

The disappointments

The strongest lesson of the past 3 decades is that nutrient supplements given to broad populations to prevent chronic disease have often failed, and sometimes caused harm.

Antioxidants. Beta carotene supplementation increased lung cancer in smokers in 2 large trials. A systematic review of antioxidant supplement trials found no reduction in mortality overall, and possible increases with beta carotene, vitamin A and vitamin E.

Vitamin D. The VITAL trial, which gave vitamin D to more than 25,000 adults not selected for deficiency, found no reduction in cancer or major cardiovascular events. Other large trials have produced similar results.

Vitamin E and selenium. A large trial of vitamin E and selenium to prevent prostate cancer found no benefit, and later follow up suggested increased prostate cancer risk with vitamin E.

B vitamins for homocysteine. Lowering homocysteine with B vitamins did not reduce cardiovascular events in several trials, despite homocysteine being associated with cardiovascular risk.

High dose vitamin C in cancer. Early reports of benefit from high dose vitamin C in cancer were not confirmed in controlled trials of oral vitamin C. Intravenous vitamin C remains under investigation but is not established treatment.

These findings share a pattern. A nutrient associated with better health in observational studies, or with a plausible mechanism, did not produce benefit when given as a supplement to people who were not deficient. Observational associations often reflect the whole diet and lifestyle of people with high intakes, not the effect of the isolated nutrient.

Principles for practising nutritional medicine well

1. Identify a specific indication. A confirmed deficiency, a condition with trial evidence, or an established need such as folic acid before conception.
2. Prefer food where it meets the need. Whole diets deliver nutrients in combinations and forms that isolated supplements do not replicate.
3. Dose to the indication. Treatment doses for deficiency differ from maintenance doses; high doses without an indication carry risks.
4. Check interactions. Nutrients interact with medicines and with each other: calcium and iron with levothyroxine, vitamin K with warfarin, high zinc with copper status.
5. Monitor and stop. Recheck levels, review benefit and stop supplements that are not helping.
6. Consider quality. Product quality and content vary, particularly outside well regulated markets.
7. Be honest about evidence. Explain which uses are established and which are speculative.

Intravenous nutrient therapy

Intravenous vitamin and mineral infusions are marketed widely for energy, immunity, hangovers and wellbeing. Outside specific medical indications, such as severe deficiency, malabsorption or iron deficiency in certain conditions, evidence of benefit is lacking, and intravenous administration carries risks including infection, vein damage, fluid overload and electrolyte disturbance. Practitioners should be cautious about recommending such therapies and alert to them in patients’ histories.

An illustrative case

A 55 year old woman brings a bag containing 14 supplements recommended over several years by different sources, including high dose vitamin E, beta carotene, several antioxidants, a high dose B6 product and vitamin D at a dose well above maintenance. She reports tingling in her feet. Her doctor finds a raised B6 level and a vitamin D level above the target range. The supplements are reviewed one by one. The B6 and most antioxidants are stopped, the vitamin D dose is reduced, and she continues only those with a clear indication. Over the following months her tingling improves. The most important nutritional intervention in her case was subtraction.

The discipline that makes nutrition powerful

Nutritional medicine is at its most effective when it is precise: the right nutrient, for the right indication, at the right dose, for the right duration. That precision is what distinguishes it from the indiscriminate supplementation that has given the field a mixed reputation, and it is what allows practitioners to use nutrients as the powerful clinical tools they can be.