Should You Take Supplements? What Your Blood Test Results Say

Quick answer

Base your supplements on test results, not marketing claims. The supplements with the strongest evidence, and the clearest test to guide them, are vitamin D, B12, folate, iron, magnesium, omega-3, and creatine for athletes. Most other "wellness" supplements lack strong evidence or a clear way to track them.

A simple framework

Ask three questions before taking any supplement.

1. Does it fix a real gap, or meet a proven need?
2. Does it offer a real benefit, at a safe dose?
3. Can you track whether it worked?

If you answer yes to all three, it is worth considering. If any answer is no, it is usually safe to skip.

Supplements with strong evidence and a clear test

Vitamin D

• Test: 25-OH vitamin D.
• When to take it: any result under 40 ng/mL.
• Dose: 1,000 to 5,000 IU a day, based on your level.
• Retest: at 12 weeks.

Vitamin B12

• Test: serum B12.
• When to take it: B12 under 500 pg/mL with symptoms, or any confirmed low result.
• Dose: 1,000 mcg a day of methylcobalamin, a well absorbed form. Shots may help severe cases.
• Retest: at 12 weeks.

Folate

• Test: serum folate.
• When to take it: under 9 ng/mL, or a high homocysteine result.
• Dose: 400 to 800 mcg of methylated folate.
• Special note: all women who could become pregnant benefit from 400 mcg before conception.

Iron (checked through ferritin)

• Test: ferritin, checked alongside hs-CRP.
• When to take it: ferritin under 50 ng/mL with symptoms, or under 30 in any case.
• Dose: 65 mg of elemental iron, daily or every other day.
• Retest: at 12 weeks.

Magnesium

• Test: serum or RBC magnesium.
• When to take it: symptoms such as cramps, poor sleep, or migraines, or a known low intake.
• Dose: 200 to 400 mg a day. Glycinate for sleep, citrate for constipation.

Omega-3 (EPA and DHA)

• Test: omega-3 index.
• When to take it: a score under 8%, or low fish intake.
• Dose: 1,000 to 2,000 mg combined a day.
• Retest: at 16 weeks or later.

Creatine, for athletic performance

• Test: none needed.
• When to take it: for strength training or performance goals.
• Dose: 3 to 5 g a day.
• Effect: small but steady gains in strength and power.

Supplements with moderate evidence

Vitamin K2, alongside vitamin D

Useful if you take a high dose of vitamin D. Some evidence for bone and heart health. A typical dose is 90 to 180 mcg a day.

Curcumin

An anti-inflammatory compound with weak natural absorption. Choose a product built for better absorption. A typical dose is 500 to 1,000 mg, twice a day.

CoQ10

May help with muscle aches on statins. Levels also drop with age. A typical dose is 100 to 200 mg a day.

Probiotics

Useful for specific issues, such as diarrhea after antibiotics. General "gut health" claims rest on weaker evidence. The specific strain matters more than the word "probiotic."

Glucosamine and chondroitin

Modest evidence for joint pain from arthritis. Try it for 8 to 12 weeks to see if it helps you.

Supplements with weak or unclear evidence

These are heavily marketed, but the evidence behind them is thin:

• Multivitamins, at best a small benefit.
• Most "adaptogens," though ashwagandha shows some promise for stress.
• Collagen, modest evidence for skin and joints.
• BCAAs, branched-chain amino acids. Enough protein in your diet usually covers this already.
• Most "immune boosting" products, including elderberry and echinacea.
• High-dose antioxidant pills, such as vitamin E or vitamin C, which can even cause harm at very high doses.
• "Detox" or "cleanse" products.

This does not mean these never help anyone. But the evidence is thin, and the cost adds up.

Supplements to be careful with

• High-dose single antioxidants. Some large studies link high-dose vitamin E or beta-carotene to worse outcomes in certain groups.
• High-dose niacin. Despite improving cholesterol numbers, it has not shown a clear heart benefit in trials.
• Iron, without a confirmed low level. This risks iron overload, especially in men and women past menopause.
• High-dose calcium supplements. These may raise heart risk in some groups. Food sources are usually the safer choice.
• Herbal weight loss products. Some have caused liver damage.
• "Test boosters" and unregulated performance products. These can carry real heart and liver risks.

How to use your blood test to choose supplements

Step 1: Get a full panel

Include vitamin D, B12, folate, ferritin, magnesium, and, where available, the omega-3 index. You can book a full panel here to get all of these in one draw.

Step 2: Spot the real gaps

Anything below the healthy target, paired with symptoms, is worth a closer look.

Step 3: Start with the biggest wins

For most adults here, vitamin D, iron in women, and magnesium tend to matter most. These are also the nutrient gaps found most often among Filipinos.

Step 4: Add one or two at a time

This makes it easier to tell what is actually working.

Step 5: Retest at 12 weeks

Confirm it is working, and adjust the dose if needed.

Step 6: Stop what you no longer need

Once a level reaches the healthy target and stays there, a lower maintenance dose is usually enough.

Choosing a quality brand

The supplement industry has weak rules. Look for:

• Outside testing, such as NSF or USP, which checks content and purity.
• A reasonable dose, since a very high dose is rarely needed.
• Active forms, such as methylated B vitamins, vitamin D3, and magnesium glycinate.
• No hidden blends that mask how much of each ingredient you are getting.

How &you Labs supports your supplement choices

Every &you Labs report includes clear supplement guidance based on your own results. This means a dose for any real gap, and a suggested retest date. The goal is a plan you can actually act on, not just a list of numbers. See the full list of markers we test on our biomarker page.

Frequently asked questions

Should everyone take a multivitamin?

For most adults eating a varied diet, it offers little clear benefit. Some groups, such as pregnant women or people with limited diets, benefit more. Large trials have not shown a clear benefit for most healthy adults.

Is food always better than a supplement?

Usually, yes. Food gives you other helpful compounds along with the nutrient itself. But for a confirmed gap, a supplement reaches a helpful dose faster and more reliably.

How do I pick a trustworthy brand?

Look for outside testing seals and sensible doses. Independent supplement testing organizations also check many brands and publish what they find.

Can I take too many supplements at once?

Yes. Supplements can interact with each other, and with your medicines. Share your full list with your doctor.

Should I take supplements during pregnancy?

Pregnancy has its own guidelines. This usually means a prenatal vitamin with folate, iron when needed, vitamin D, and sometimes DHA. Talk with your obstetrician about your own plan.

Key takeaways

• Choose supplements based on test results and real need, not marketing claims.
• The strongest evidence supports vitamin D, B12, folate, iron when ferritin is under 50, magnesium, omega-3, and creatine for athletes.
• Many popular supplements have weak or unclear evidence behind them.
• Look for outside testing, and skip products with hidden ingredient blends.
• Start with one or two, retest at 12 weeks, and adjust based on your results.