Working out what to take is needlessly hard.

Short sleep measurably degrades immune function Peer-reviewed review

Sleep deprivation has documented effects on immune-cell numbers, immune-cell function, and cytokine production — enough that researchers treat sleep as part of the immune system rather than a bystander. The classic review is Bryant, Trinder & Curtis (2004), though it sits behind a paywall. For a free and more recent treatment, see Garbarino et al. (2021) in Communications Biology, which is open access.

There is also decent evidence that chronic partial sleep loss — the four hours you quietly give up every weeknight — may do more damage than one dramatic all-nighter.

Micronutrients matter — but "boosting" immunity isn't a thing Clinical guidance

Iron, vitamins A, C, D and E, and zinc are all genuinely needed for immune cells to grow and work, and Mayo Clinic Health System lists food sources for each.

The same article makes a point worth quoting against myself: the idea of boosting immunity through diet is flawed, because boosting means pushing above normal. What food does is prevent the immunodeficiency that comes from malnutrition and micronutrient gaps. That's a smaller and more honest claim than most supplement marketing makes — mine included.

Chronic stress really does suppress immunity Clinical guidance

Per Cleveland Clinic, short bursts of cortisol can actually help by limiting inflammation. The problem is sustained stress: over time it decreases lymphocytes — the white cells that fight infection — and lower lymphocyte counts leave you more vulnerable to ordinary viruses.

Regular exercise can have a positive effect on stress. Mayo Clinic on exercise and stress

Multivitamin Common Sense

• 1 dose daily
• Use caution with >100% DV

A plain multivitamin is reasonable insurance against dietary gaps. Brand matters less than the USP mark. I use a the costco brand. Other brands with good reputations are Pure Encapsulations and Thorne.

Mayo's dietitians are specific on the ceiling: a general multivitamin providing no more than 100% of the recommended daily allowance is generally safe, and you should use caution with mega-doses above that level. Mega doses can potentially add no benefit and can do harm. If you feel the need to go with a vitamin that has doses far above 100%, check with your doctor and pharmacist to ensure it's safe.

Vitamin D Good Evidence

• 2,000–4,000 IU daily
• NIH upper limit 4,000 IU
• Ask for a blood test

This is the supplement with the clearest rationale in a northern climate. Deficiency is genuinely common: an NHANES analysis by Forrest & Stuhldreher (2011) put US adult deficiency at 41.6%, rising to 82.1% among Black Americans and 69.2% among Hispanic Americans. More recent NHANES data through 2018 shows a similar picture, with winter the worst season.

At northern-Indiana latitudes your skin makes little to no vitamin D from sunlight through the winter months, which is why the season matters more here than the sunshine does. Harvard's Nutrition Source covers the immune role.

The useful move is testing, not guessing. Ask for a 25-hydroxyvitamin D level at your next physical and dose from the result. 2,000 IU is a reasonable place to start while you wait; the NIH tolerable upper limit for adults is 4,000 IU, and your doctor may go higher on purpose if your level is low.

Vitamin C Real and safe

• 1,000 mg daily
• Upper limit 2,000 mg

There is debate on whether Vitamin C is useful in supporting your immune system. However, it is viewed as generally safe to take and may help your immune system fight off infections.

Safety: the upper limit is 2,000 mg/day, set to avoid diarrhoea and stomach upset. If you're prone to kidney stones, consider avoiding doses at or above 1,000 mg/day.

B complex Not harmful, might help

• 1 tablet daily
• Harmless side effect: bright yellow urine

Vitamin B Complex tablets typically contain 8 vitamins that are types of Vitamin B. Some research has shown a positive effect on brain function with Vitmain B supplementation. A known side effect of vitamin b supplementation is that your urine may turn neon in color after taking the supplement.

The neon-yellow urine is riboflavin (B2) doing exactly what it should. Harmless.

Omega-3 / fish oil Qualified claim only

• 1–2 g daily
• Or two oily fish meals a week

There are various benefits of Omega 3 supplementation that are emerging in research including a reduction in age-related degredation and general cognitive benefits.

Safety - If you take blood thinners, clear fish oil with your doctor first.

Zinc — for colds, not for every day Situational

• At symptom onset only
• Adult upper limit 40 mg
• Check your multivitamin first

Zinc can shorten a cold in some circumstances, per Mayo Clinic — but the studies that show it use syrup or lozenges started within about 24 hours of the first symptom, not daily maintenance dosing. Most people eating a varied diet already get enough; the adult RDA is 11 mg for men and 8 mg for women.

Never use zinc nasal sprays or swabs. Intranasal zinc has been linked to loss of the sense of smell, which can be long-lasting and may never come back.

Most multivitamins already contain zinc, so add up your total before adding more — the adult upper limit is 40 mg/day, above which you get stomach upset, and long-term excess causes copper deficiency. And zinc blocks absorption of quinolone and tetracycline antibiotics, so separate the doses if you're on either.