Vitamins: measure first, don’t guess

It is a common scene: a multivitamin, vitamin C “just in case,” something for tiredness a friend recommended, another bottle ordered online. You have been taking them for months and you do not know whether they do anything, whether you already have too much, or whether the thing you actually need is missing.

Guessing has a cost. You spend money on products you may not need. And the symptom that sent you shopping, such as tiredness, tingling, bone pain or weakness, may have a cause a bottle does not fix and a doctor can look for. This guide explains what can be measured, what cannot, and how to decide with information instead of assumptions.

Measuring everything blindly is not better than measuring for a reason. In 2021 the USPSTF concluded that the evidence is insufficient to recommend for or against vitamin D testing in adults without symptoms. That does not mean the test is bad; it means that without a reason, we do not know whether testing helps.

Separate from that conclusion: when a test is ordered without a clear question, a result can be flagged by chance and lead to more tests and worry. So the useful question is not “how many vitamins can I measure?” but “what decision will this result change?”

Vitamins are not harmless just because they are vitamins. MedlinePlus warns that too much vitamin D is uncommon but possible, almost always from supplements, and can cause nausea, vomiting, poor appetite, constipation, weakness and weight loss; with toxicity, the excess can damage organs and blood vessels.

A low level is not always fixed with a bottle, either. Sometimes the cause is something else: an absorption problem, a medicine or a condition that needs treatment. That is why it helps to measure before starting and to recheck, if your doctor advises it, to see whether the plan is working.

Supplements are not approved to treat, cure or prevent disease, and labels cannot claim they do. A supplement can help correct a confirmed deficiency, but it does not replace the diagnosis and treatment of a condition.

Do not choose a dose yourself or start high-dose products to chase a result, especially in pregnancy or for a child, without talking to a doctor first.

In a video visit, Dr. Diana Nieves Castro, a licensed general practice physician in Puerto Rico, starts with a medical assessment: your history, your symptoms and your medicines. Then she reviews everything you take: prescriptions, over-the-counter medicines, vitamins, supplements, herbs and teas. The approach is lifestyle-first within medical care: sleep, food, movement and stress, and labs when there is a reason to order them.

Have the bottles or a photo of each label on hand, with the dose and how often you take it. When clinically appropriate, the doctor gives you a lab order for a lab near you, and when you have results she goes over them with you in a follow-up visit, which is for existing patients. To understand a report on your own, read how to read lab results.

If you are in Puerto Rico, you can reserve an online visit and bring your bottles to the first review. The doctor does not sell supplements or products. To see how this fits into overall care, read what lifestyle medicine is.

Do not wait or keep trying bottles if you have unexplained tiredness, numbness or tingling that does not go away, weakness, loss of balance, confusion, bone or muscle pain, or changes in mood: these can have a cause that is evaluated with a doctor and labs. Do not change, delay or stop a prescribed medicine on your own, or skip vaccines or screenings, without talking to a doctor first.

If you have chest pain, shortness of breath, fainting, sudden confusion, weakness on one side of the body or bleeding that does not stop, call 911 or go to the emergency room. If you feel very sad or anxious or are thinking of hurting yourself, call or text 988 or the Línea PAS 1-800-981-0023.

Visits are for people physically in Puerto Rico during the visit. This guide is information, not a diagnosis or treatment, and it does not replace your doctor.