Vitamins are 13 compounds that are vital for optimal health (hence vit-amin), but cannot be made in large quantities. We typically consume vitamins through whole foods or fortified foods. And for the past 80 years, vitamins have been synthesized and made available as supplements our diets.
The idea of using foods to heal is nothing new; over 2,000 years ago, the Egyptians learned that feeding liver, now known to be high in Vitamin A, to a person with night blindness could cure the condition. Similarly, in the 1700s, sailors suffering from scurvy, now known to be a vitamin C deficiency, could reverse their symptoms by consuming high levels of citrus fruits.
The availability of synthesized vitamins has shifted concern from vitamin deficiencies to the risk of vitamin excess. Last week, for example, research showing that Vitamin B3 (niacin) may be harmful when given in high doses to patients with abnormal cholesterol levels made headlines.
Are there other examples? Just how worried do we need to be about our vitamins?
A deficiency of Vitamin B3 causes a disease called pellagra but niacin has been used for over 50 years to lower total cholesterol levels while raising HDL cholesterol concentrations. Generally we only need about 20 to 35 mg a day of niacin, but doses of up to 3,000 mg a day or more are used to control cholesterol.
Niacin has been used for decades, but it was approved for use at a time when monitoring side effects was less common. Two scientific studies published this month showed no cardiovascular benefit to prescribing niacin. The studies did demonstrate, however that niacin increased the risk of ulcers by 28%, muscle damage and gout by 26%, skin problems by 67%, infections by 22%, and bleeding by 38%! Patients on niacin were 32% more likely to be diagnosed as having diabetes.
2. Vitamin D
Vitamin D can be made after exposure to sunlight. It's necessary for the absorption of calcium, iron, magnesium, zinc and phosphorus and we're starting to understand that it helps prevent heart disease and cancer.
Many people are low in vitamin D and routine supplementation is increasingly common and helpful. However, the dose determines the poison and I increasingly see patients advised to take enormous daily doses (10,000 IU chronically or more), which drive their blood levels to excessive levels.
Because vitamin D is a fat soluble vitamin (unlike C and B vitamins, which are not stored in tissues long-term) it will remain in the body for long periods of time if given in excess. Vitamin D overdosing may cause high blood calcium levels, leading to poor appetite, nausea and vomiting. Kidney stones are a risk.
I recently cared for a patient who'd been told to take enormous doses of vitamin D. This led to a blood level over 300 ng/mL (compared to an optimal level of between 40 and 80 ng/mL) and a severe illness requiring referral and hospitalization at the Mayo Clinic.
3. Vitamin A
Vitamin A is another fat soluble vitamin required for vision, immune health and reproduction. We get vitamin A mostly from dairy, fish and meat (as preformed retinols) and from plants as the provitamin beta-carotene. Blood levels of vitamin A are not routinely available to clinicians.
You don't have to worry about getting too much vitamin A from plant-sources, as beta-carotene will not be converted to the active vitamin if there are already enough stores in the body. Be wary, however, of getting too much vitamin A from diet or excessive supplements (i.e. cod liver oil). Excess intake of vitamin A can cause headaches, dizziness, nausea, and even death. Generally under 10,000 units a day are safe for most people.
4. Vitamin E
This is the last fat-soluble vitamin and it acts as an antioxidant. It also boosts the immune system and prevents harmful blood clotting.
Excessive dosing of vitamin E has been linked to an increase of prostate cancers and lung cancers. Vitamin E can also increase the risk of bleeding if given at high doses, particularly with other blood thinners.
Overdosing on vitamin E only happens from supplements in excess of 1,500 IU a day for natural forms and 1,000 IU a day for synthetic forms of vitamin E.
Vitamin dosing is an example of the U-shaped curve that describes many bodily pathways. This is sometimes referred to as the "Goldilocks phenomenon" as too little or too much of something may cause harm and knowing the right amount is key.
These vitamins teach us that whole foods grown with organic farming practices are the optimal way to meet our nutritional needs. Sure, supplements are useful for some conditions, but more is not necessarily better.
If you're going to get too much of a good thing, follow the lead of Salvador Dali who said, “Some days I think I am going to die from an overdose of satisfaction.”