Vitamin D: The Sunshine Vitamin You Are Probably Missing
Vitamin D behaves less like a vitamin than like a hormone, and the post's framing is that it influences genes throughout the body. Deficiency is common, on the post's account, and commoner among older adults, people with darker skin, and people living at northern latitudes. It matters for calcium absorption, immune function, mood and muscle strength. Sunlight, food and supplements are the three sources. A blood test is the only way to know where you sit, and the post names the one to ask for: 25-hydroxyvitamin D.
The Vitamin D Crisis
Vitamin D deficiency is one of the most common nutritional deficiencies worldwide. An estimated 42% of American adults are vitamin D deficient, with rates even higher among older adults, people with darker skin, and those living in northern latitudes.
This matters because vitamin D is not just a vitamin. It functions as a hormone and influences over 200 genes in your body.
Why Vitamin D Matters
Bone Health
Vitamin D is essential for calcium absorption. Without adequate vitamin D, only 10-15% of dietary calcium is absorbed, compared to 30-40% with sufficient levels. This directly impacts bone density and fracture risk.
Immune Function
Vitamin D activates T cells, your immune system's first responders. Multiple studies link low vitamin D with increased susceptibility to respiratory infections, autoimmune conditions, and certain cancers.
Mental Health
Research shows a strong correlation between vitamin D levels and mood. Low levels are associated with increased risk of depression and seasonal affective disorder.
Muscle Function
Vitamin D deficiency contributes to muscle weakness and pain, particularly in older adults. Adequate levels support muscle strength and reduce fall risk.
How Much Do You Need?
The recommended dietary allowance varies by age:
- Infants (0-12 months): 400 IU daily
- Children and adults (1-70): 600 IU daily
- Adults over 70: 800 IU daily
However, many experts argue these recommendations are too low. The Endocrine Society suggests that 1,000-2,000 IU daily may be more appropriate for maintaining optimal blood levels of 30-50 ng/mL.
Getting Enough Vitamin D
Sunlight
Your body produces vitamin D when skin is exposed to UVB rays. Aim for 10-20 minutes of midday sun on arms and legs, 2-3 times per week. Factors that reduce production:
- Sunscreen (SPF 30 blocks 97% of UVB)
- Dark skin (more melanin means slower production)
- Northern latitudes (especially November through March)
- Glass windows (UVB does not penetrate glass)
Food Sources
Few foods naturally contain vitamin D:
- Fatty fish (salmon, mackerel, sardines): 400-600 IU per serving
- Egg yolks: 40 IU each
- Fortified milk and orange juice: 100 IU per cup
- Mushrooms exposed to UV light: 400 IU per serving
Supplementation
For many people, supplementation is necessary to reach optimal levels. Vitamin D3 (cholecalciferol) is more effective than D2 (ergocalciferol). Take with a meal containing fat for better absorption.
Tracking With LifeWell
Use the vitals tracking feature to:
- Log vitamin D supplement intake as part of your medication tracker
- Track sun exposure time
- Record lab results when you get your levels tested
- Set reminders for daily supplementation
Get Tested
The only way to know your vitamin D status is a blood test (25-hydroxyvitamin D). Ask your doctor to include it in your next routine blood work, especially if you live in a northern climate, spend most time indoors, or have darker skin.
Elsewhere on LifeWell
- Privacy — What LifeWell stores, where it sits, and who can read it back.
- Plans — What the free plan includes, and what each paid one adds.
- Export everything — Your whole record leaves in one file, on any plan, without giving a reason.
What people use it for
Add the supplement on the medications list with "This is…
Add the supplement on the medications list with "This is a vitamin or supplement" ticked, and it appears under the vitamins filter with today's dose.
Turn on "Remind me about this one" at the times you…
Turn on "Remind me about this one" at the times you actually take it. Quiet hours hold a reminder rather than dropping it. A late one still arrives afterwards.
Record the blood result
Record the blood result at `/health/lab-results`: name the test and say what unit it is reported in, so every result of it sits beside the last one. The unit matters.
Take the list to the appointment
Take the list to the appointment. Only you ever see it.
Questions
How do I know whether I am low?
A blood test, and only a blood test. The post names it as 25-hydroxyvitamin D and suggests adding it to routine blood work, particularly if you live in a northern climate, spend most of your time indoors or have darker skin. LifeWell records what the laboratory told you. It does not interpret it, and it has no connection to any laboratory.
How much should I take?
The post sets out the recommended dietary allowance by age, at 400 IU for infants, 600 IU for ages 1 to 70 and 800 IU after that, and it notes the Endocrine Society's view that 1,000 to 2,000 IU may suit adults better. Which of those applies to you is a medical question. LifeWell does not suggest doses and never will.
Can I get enough of it from the sun?
Sometimes, and the post is specific about what stops it: sunscreen at SPF 30 blocks 97% of UVB, more melanin slows production, glass blocks UVB entirely, and a northern winter stops it for months. Its own guide is 10 to 20 minutes of midday sun on arms and legs, two or three times a week.
Which foods have it?
Few of them, which is the post's point. It lists fatty fish at 400 to 600 IU a serving, egg yolks at about 40 IU each, fortified milk and orange juice at 100 IU a cup, and mushrooms exposed to UV light at 400 IU. Reaching the higher numbers on food alone is difficult without one of the fortified sources.
Can I keep the supplement and the result in one place?
Yes, on two pages of the same record. A supplement goes on the medications list with "This is a vitamin or supplement" ticked, and it then appears under the vitamins filter with today's dose and whatever reminder you set on it. A blood result goes on the lab results page under the test's own name and the unit it was reported in, so every result of that test sits beside the last one.
Does LifeWell check my supplements for interactions?
No, and the medication pages say so before you can wonder. Every name, dose and time on the page was typed by you; LifeWell does not suggest doses, does not check interactions, does not know your prescription, and will never tell you that a missed dose is fine or that it is serious. Those are medical judgements and they belong to your doctor or pharmacist.
Will it tell me whether a result is normal?
No. The lab results page states its own position in three refusals: LifeWell does not interpret a result, does not say whether one is normal, and has no connection to any laboratory. What it holds is the results you have had, in your own file, with the date they were taken. The reading belongs to whoever ordered the test.
By Ahsan Mahmood · updated 2025-11-30
Open Vitamin D: The Sunshine Vitamin You Are Probably Missing on LifeWell