Vitamins: Evidence, Benefits and Considerations
Vitamins are essential for maintaining health and preventing disease. Despite their importance, there’s widespread confusion about which supplements truly help and which may be unnecessary or even harmful. This evidence-based guide outlines what we currently know.
Water-Soluble vs Fat-Soluble Vitamins
Water-Soluble Vitamins
These dissolve in water and are not stored extensively in the body. Excess amounts are usually excreted in urine. While toxicity risk is lower, very high doses can still be harmful.
Examples: Vitamin C, and all B vitamins (B1–B12)
Note: Require regular intake due to limited storage.
Fat-Soluble Vitamins
These dissolve in fat and are stored in body tissues and the liver. They are eliminated more slowly, so toxicity is a greater concern if taken in excess.
Examples: Vitamins A, D, E, and K
Where the Evidence Is Strong
Vitamin D
Supports bone health, immune regulation, and may reduce risk of some chronic illnesses.
Who benefits: People with low sun exposure, older adults, darker skin tones, or absorption issues.
Vitamin B12
Prevents certain types of anaemia, supports the nervous system, and aids cell metabolism.
Who benefits: Adults over 50, vegetarians, vegans, and those with gut absorption problems.
Folic Acid (B9)
Crucial for preventing neural tube defects in pregnancy and supports DNA synthesis.
Who benefits: Women of childbearing age, especially before and during early pregnancy.
Limited or Context-Dependent Evidence
Vitamin C
May reduce the duration of colds and supports immune function, but doesn’t prevent illness. High doses have limited benefit and can cause side effects.
Vitamin E
Has antioxidant effects and may help in some conditions. However, high-dose supplementation has shown little benefit in the general population and may interact with certain medicines.
Multivitamins
Can be useful in those with poor diets or multiple low-level deficiencies. They are not a substitute for a balanced diet and have limited impact on chronic disease outcomes.
Where Evidence Is Lacking or Risk May Outweigh Benefit
Vitamin A (as retinol)
Essential for vision and immunity, but easily over-consumed through supplements—especially during pregnancy.
High-Dose B Vitamins
Important in metabolism and nerve function, but high doses (unless deficient) show little benefit and may mask B12 deficiency if B9 is taken in excess.
Clinical Considerations
Personalised Supplementation
Blood tests can identify specific deficiencies
Health history helps guide individual needs
Life stage matters—needs vary in pregnancy, ageing and childhood
Food vs Supplements
Whole foods first: Vitamins are typically better absorbed this way
Form and source: Some supplements are more bioavailable than others
Quality control: Choose well-regulated, tested products
Interactions and Contraindications
Medication interactions: Some vitamins affect how medicines work
Medical conditions: Certain illnesses may limit safe supplement use
Surgery: Some should be stopped before operations
Dr Crespo’s Thoughts
Vitamin supplements can be helpful when used correctly, especially to correct specific deficiencies or during key life stages. But more isn’t always better—some can do harm. I recommend a food-first approach, guided by testing and clinical context. If you’re unsure, speak to a healthcare professional before starting any supplement regimen.
1. Emphasizing nutrient-dense whole foods as the primary source of vitamins
2. Using targeted supplementation based on individual risk factors, laboratory testing, and clinical assessment
3. Regular monitoring and adjustment of supplementation regimens
4. Consulting healthcare providers before beginning supplements, particularly for those with existing health conditions or taking medications
By following these evidence-based guidelines, individuals can make informed decisions about vitamin supplementation that maximize benefits while minimizing potential risks.
