Doctors warn about the intake of these 5 nutrients.

 In addition to eating more fruits and vegetables, some people also take health supplements to boost their immunity, but in moderation, to avoid putting the cart before the horse and causing health problems!

Although most people can eat their fill every day, and some even become overweight, deficiencies in certain micronutrients can still occur. According to a 2025 study published in the New England Journal of Medicine, the following situations should be paid special attention to:

1. Vitamin D – Sunlight is Also Important

Vitamin D is one of the most common nutrient deficiencies in the United States. A recent survey found that more than one-fifth of people are vitamin D deficient, and deficiency is more likely to occur in young people, Black people, those who don't drink milk regularly, or those who don't get enough sunlight. The American Medical Association considers a blood concentration of 50 nmol/L or higher to be sufficient, and below 30 nmol/L to be deficient.

Interestingly, even with multivitamins, 26% of people are still not enough, and 5 to 7% are deficient. Therefore, supplements alone are not enough; diet (such as dairy products) and sunlight exposure are also crucial.

2. Vitamin B12 – Vegetarians Should Pay Special Attention

Found only in animal-based foods such as meat, fish, milk, and eggs, vegans are prone to B12 deficiency without additional supplementation, leading to anemia, nerve problems, or fatigue. It is also common in the elderly, those who have undergone gastrectomy, or those with poor gastrointestinal absorption. Data shows that approximately 2% to 4% of Americans have a significant deficiency.

3. Antioxidants – More Isn't Always Better

While once touted for their anti-cancer, anti-aging, and heart-protective properties, scientific research has not proven that high-dose supplementation is beneficial. In fact, it may cause side effects. For example, high doses of vitamin A increase the risk of fractures and prostate cancer, while vitamin E may increase infection and mortality rates. Relatively speaking, certain formulas, such as combinations of vitamin C, vitamin E, zinc, and lutein, are helpful for patients with macular degeneration. Of course, consuming natural fruits and vegetables is the best source of antioxidants.

4. Iron – High Risk for Adolescent Girls and Pregnant Women

Nearly 40% of American adolescent girls have iron deficiency, which can develop into iron-deficiency anemia. Those with heavy menstrual bleeding, pregnant women, or vegetarians are particularly susceptible. In fact, the level of "ferritin" in the blood can indicate whether the body is iron deficient. In terms of diet, "heme iron" from meat has the best absorption rate. If needed, iron supplements can be taken, but large doses can easily lead to constipation or nausea.

5. Folic Acid—The Gatekeeper of Neural Tube Defects

Since 1998, the United States has mandated the fortification of folic acid in flour and rice, successfully reducing the incidence of neural tube defects in fetuses. Therefore, folic acid deficiency is now quite rare. However, excessive folic acid supplementation (>1000 micrograms/day) may affect vitamin B12 metabolism, so indiscriminate supplementation is not advisable.

As for how to take supplements, the American Academy of Nutrition and Dietetics recommends considering supplements only if dietary intake is insufficient. Certain groups are more prone to deficiency, such as growing children, people with chronic diseases, pregnant and breastfeeding women, the elderly, and vegetarians. However, it is not recommended to take supplements indiscriminately to "prevent disease," as there is currently no strong evidence to support this approach.