Why does vitamin D matter?
Vitamin D is usually thought of simply as "the bone vitamin," but it does a lot more than that. It helps your gut absorb calcium, which your body needs to build and maintain bone. It also helps muscles work properly and plays a role in regulating the immune system. When bones and muscles weaken together, balance suffers and falls become more likely, so vitamin D deserves special attention in later life. Korea's disease control agency (KDCA) notes that low vitamin D can reduce bone density and raise the risk of falls.
Why do older adults run low?
With age, the skin becomes less able to make vitamin D from sunlight, even with the same sun exposure. At the same time, many people spend more time indoors and go out less, so they get less sun to begin with. The kidneys' ability to convert vitamin D into its active form may also decline over the years. Put these together, and vitamin D is one of the nutrients most likely to fall short after 65 unless you pay attention to it.
Signs of vitamin D deficiency
A significant shortage can lead to osteomalacia (softening of the bones), and may cause bone pain, muscle weakness, muscle aches, and a general sense of tiredness. In older adults, however, the symptoms are often vague, so regular checks are more reliable than waiting for symptoms.
How much do you need each day after 65?
Recommendations differ a little from country to country:
- Korea: The Dietary Reference Intakes for Koreans (Ministry of Health and Welfare and the Korean Nutrition Society) set 15 µg (600 IU) a day for adults 65 and older, up from 10 µg for ages 19–64; we read this as reflecting how skin production declines with age. This is an "adequate intake," set from the intake of healthy people because the evidence was not strong enough to calculate a precise requirement.
- United States: The NIH recommends 20 µg (800 IU) a day for adults 71 and older.
Either way, the message is the same: older adults need more than younger adults do.
The upper limit, and the risk of taking too much
Vitamin D is fat-soluble and builds up in the body, so more is not better. The upper limit is 100 µg (4,000 IU) a day, both in the Korean guidelines and in the US. Taking far more than this over a long period can cause hypercalcemia (too much calcium in the blood), with symptoms such as nausea, vomiting, poor appetite, and muscle weakness. If you take a supplement, check the dose on the label, and make sure it does not overlap with vitamin D in your other supplements, such as a multivitamin or a calcium tablet.
What blood level counts as normal?
Vitamin D status is measured as 25-hydroxyvitamin D [25(OH)D] in the blood. What counts as "normal," however, differs between organizations, so the same number may be explained differently by different doctors.
| Blood 25(OH)D | Interpretation by the NIH Office of Dietary Supplements |
|---|---|
| Below 12 ng/mL (30 nmol/L) | Deficient; risk of bone disease such as osteomalacia |
| 12–20 ng/mL | Possibly inadequate for bone health in most people |
| 20 ng/mL (50 nmol/L) or above | Adequate for most people |
| Above 50 ng/mL (125 nmol/L) | Possible adverse effects from excess |
Many clinics, including in Korea, use 30 ng/mL or above as "sufficient" (from the Endocrine Society's 2011 guideline). In its 2024 guideline, the Endocrine Society said there is not enough evidence to aim for a specific level and recommended against routine vitamin D blood tests for adults under 75 without symptoms or risk factors. The same guideline suggested that adults 75 and older consider vitamin D supplementation at recommended levels without testing.
Do vitamin D supplements prevent falls and fractures?
Despite the common expectation that vitamin D strengthens bones and prevents fractures and falls, large studies in older adults who were not deficient did not show this.
- VITAL fracture study (NEJM, 2022): About 26,000 men 50+ and women 55+ took 2,000 IU a day for over five years on average, with no reduction in total or hip fractures compared with placebo.
- US Preventive Services Task Force (2024): Recommends against vitamin D supplementation to prevent falls in community-dwelling adults 65 and older.
In other words, vitamin D matters most for people who are low; there is no evidence that taking more when you already have enough reduces falls or fractures. For fall prevention, add proven approaches such as balance exercises. If you are being treated for osteoporosis or have been diagnosed as deficient, follow the dose your doctor sets.
When to see a doctor
If you have ongoing bone pain or muscle weakness, unexplained fatigue that will not go away, or you have fallen several times recently, ask your doctor about a blood test to check your vitamin D level. If you have kidney or liver disease or take certain medications, talk to your care team before starting a supplement.
Please keep in mind
- This article is based on information checked as of the date shown at the top. New research or changes in official guidelines may change the details, so please use it as a reference rather than taking it as definitive.
- For an accurate diagnosis and advice about your health, please see a doctor in person.