Vitamin D
Many Americans Have An Insufficient Level of Vitamin D
Blocking the sun can impair skin production of vitamin D
But failure to block the sun can result in skin cancer
Easy solution: diet and supplements
Sun Safety vs. Vitamin D
Human skin stores up a precursor of vitamin D. This precursor can be converted to vitamin D and then absorbed into the body, but this conversion only happens when the skin is exposed to the sun’s UVB rays.
Unfortunately, the ultraviolet rays that stimulate vitamin D production are the same ones that cause sunburn and skin cancer.
This becomes a concern to champions of skin cancer prevention because very careful sun protection could reduce vitamin D production, possibly resulting in deficiency unless the sun-safe individual takes a vitamin D supplement.
Vitamin D Deficiency
Deficiency can cause rickets in children, and osteoporosis in adults. An increased risk of many other ills has been associated with insufficient vitamin D levels, however additional research is needed before they could be clearly proven to be caused by inadequate vitamin D and if so at what level would they be prevented. In the meantime it seems prudent to take reasonable measures to maintain an adequate level of vitamin D.
There are three sources of vitamin D:
1. Diet
2. Sun exposure on the skin
3. Supplements
Vitamin D in the Diet
There isn’t very much vitamin D in the typical American diet – only 4 to 5 mcg per day on average. So diet alone is usually not sufficient to supply the NIH-recommended 15 mcg per day.
A good amount of vitamin D is present in certain oily fish, 
for example, salmon, tuna, mackerel and sardines but few Americans do, or would, eat a substantial amount of these fish every day.
As a result, dietary sources alone are usually not sufficient to maintain a healthy blood level without the addition of sun exposure or a vitamin supplement.
Vitamin D From the Sun
During summer months most people acquire enough sun exposure through ordinary outdoor activities to achieve an adequate vitamin D level. Certain factors can reduce the amount of vitamin D that’s formed in response to sun exposure. These include
darkly pigmented skin, advanced age, and low UV index (e.g., winter months, rain clouds, too early or too late in the day, etc.).
The reason darkly pigmented or black skin makes less vitamin D in the sun is because it contains more melanin pigment. Melanin behaves like sunscreen. It competes against the vitamin D precursor and absorbs the sun’s UVB rays before they can stimulate the precursor to convert to vitamin D.
The challenge for older individuals is that with age the skin becomes thinner and does not hold as much of the vitamin D precursor. In addition, some elderly individuals might spend little or no time outdoors.
Sun exposure effectively produces vitamin D, but at the expense of increasing the risk of skin cancer.
Susnscreen vs. Vitamin D
Laboratory research has confirmed that when sunscreen is properly and sufficiently applied to the skin, it not only reduces sun damage, but unfortunately it also reduces vitamin D production.
Studies of real-world sunscreen use have found that it does not decrease vitamin D blood levels. There are a number of possible explanations including failure to apply sunscreen to every exposed area of skin, not using sunscreen on all occasions, using a low SPF product, not putting on enough, not re-applying every two hours, etc.
Our concern is that if people conscientiously use sunscreen and all the other recommended sun protection measures, they may be at increased risk for developing vitamin D deficiency. In contrast to the “average American,” those who very carefully practice sun safety must ensure that they maintain an adequate vitamin D level through dietary sources and supplements.
Intentional Sun Exposure Discouraged
It’s fair to wonder whether there’s some “safe” amount of sun exposure that would produce vitamin D but not increase the risk of skin cancer.
If the sun’s UV radiation were a toxin there might be an established tolerable amount. But UV is not a toxin. It’s a carcinogen. Carcinogens pose a cancer risk for humans, even at very low doses, so there is no established safe threshold.
Sun Safety for Kids strongly agrees with the NIH2 and with the American Academy of Dermatology1 which”does not recommend getting vitamin D from [intentional] sun exposure or indoor tanning.”
Vitamin D Supplements
The amount of Vitamin D in food or in a supplement is now reported as micrograms (mcg). Formerly, vitamin D was listed as International Units (IU), but IU are being phased out.
There are two forms of vitamin D: D2 and D3. Vitamin D3 is the form that human skin produces naturally in response to sun exposure. D2 is produced by fungi, including mushrooms. Both work but D3 is generally considered the better choice for humans.
Most over-the-counter supplements now are D3, but a prescription strength vitamin D is D2.
While vitamin D deficiency is a legitimate concern, care must be taken with vitamin D supplements because an excess can cause vitamin D toxicity.
Evidence is still emerging to inform the ideal safe and effective amount of vitamin D that average healthy people should ingest.
At present, the Office of Dietary Supplements at the National Institutes of Health (NIH) lists their recommended daily allowance (RDA) as 15 mcg (600 IU) per day for Americans 1 to 70 years of age.2 The NIH warns that intakes in excess of 100 mcg (4,000 IU) per day might lead to vitamin D toxicity.
Because vitamin D is fat soluble, vitamin D supplements are most effective if taken with food.
The directors of Sun Safety for Kids believe that an optimum outcome will be achieved if people practice careful sun protection year round and compensate by ingesting a sufficient daily amount of vitamin D.
Vitamin D Status
According to the NIH, “almost one out of four people have vitamin D blood levels that are too low or inadequate for bone and overall health.”2
The best measure of a person’s vitamin D status is the 25-hydroxyvitamin D [25(OH)D] blood test level.
A 25(OH)D blood level between 20 ng/ml and 50 ng/ml is considered adequate by the NIH.
A level below 12 ng/ml is too low and a level above 50 ng/ml is too high, according to the NIH.2
Serious Vitamin D toxicity occurs at blood levels above 150ng/ml.
Individual Decision on Vitamin D
Several factors go into deciding whether to take a vitamin D supplement, and if so how much.
The Endocrine Society is a professional organization directed by physicians and scientists specializing in endocrinology. Their Guidelines are based on reviewing the best available evidence provided by studies conducted to date. From their thorough 2024 review, the Endocrine Society does not find it necessary to exceed the NIH RDA of 15 mcg per day and they do not recommend routine blood testing.
However, the Endocrine Society states in their 2024 Guidelines,
“…the optimal vitamin D intake and serum 25(OH)D concentrations for disease prevention remain uncertain.”4
Lacking a defined “optimal” intake it is certainly wise to ensure getting the amount that should maintain a blood level of 20 ng/ml, which is judged to be 15 mcg (600 IU) daily for ages 1-70. But intake should remain below 100 mcg (4,000 IU) per day to avoid toxicity according to the NIH. Not only could higher doses be dangerous, there is no evidence that taking more than 100 mcg per day would yield any additional benefit.
Sun Safety for Kids is concerned about vitamin D because preventing skin cancer involves cutting out an important natural source of it. If people take careful precautions to protect themselves from the sun we worry that relying on diet alone could easily result in vitamin D deficiency.
While we await further research results, individuals who conduct very careful, consistent, and thorough sun protection might consider taking slightly more vitamin D than recommended for the general population, while taking care to stay safely below the upper limit. In other words, a dosage midway between 15 to 100 mcg per day.
While there is no clear proof of superior outcomes, there is no evidence of harm occurring to sun-safe adults who take 50 mcg (2,000 IU) daily.
Sun Safety for Kids does not make this or any specific recommendation beyond our encouragement to follow established NIH and Endocrine Society recommendations to prevent vitamin D inadequacy or deficiency.
Keep in mind that most multivitamins and calcium supplements contain vitamin D. If you are taking something like that, factor that amount into your daily total intake.
Of course it is recommended to discuss your individual circumstances with your health care provider in making an informed decision on vitamin D supplementation.
Vitamin D For Kids
Moms of infants, be aware! Even if your vitamin D status is adequate, there won’t be enough vitamin D in your breast milk to meet your baby’s needs. All breast fed babies should take a vitamin D supplement.
Vitamin D deficiency in childhood can have a terrible effect on bones, resulting in skeletal malformations known as rickets.
The NIH RDA for ages birth to 1 year is 10 mcg (400 IU).
For children 1 year and older, the RDA is the same as for adults, 15 mcg (600 IU).
Upper limits are as follows:
Birth to 6 months 25 mcg (1,000 IU)
Infants 7–12 months 38 mcg (1,500 IU)
Children 1–3 years 63 mcg (2,500 IU)
Children 4–8 years 75 mcg (3,000 IU)
Children 9–18 years 100 mcg (4,000 IU)
Adults 19 years and older 100 mcg (4,000 IU)
Pregnant and breastfeeding teens and women 100 mcg (4,000 IU)
References
- https://www.aad.org/media/stats-vitamin-d
- https://ods.od.nih.gov/factsheets/VitaminD-Consumer/
- Holick MF. Vitamin D Status: Measurement, Interpretation, and Clinical Application. Ann Epidemiol. 2008 Mar 10;19(2):73–78.
- https://www.endocrine.org/clinical-practice-guidelines/vitamin-d-for-prevention-of-disease
