The US Recommended Dietary Allowance (RDA) of vitamin D from 1989 is 200 IU.45
Yet, studies have shown that 200 IU/day has no effect on bone status.42
It has been recommended that adults may need, at a minimum, five times the RDA, or 1,000 IU, to adequately prevent bone fractures, protect against some cancers and derive other broad-ranging health benefits.45
In conclusion, the 1989 RDA of 200 IU is antiquated, and the newer 600 IU Daily Reference Intake (DRI) dose for adults older than 70 is still not adequate.45
It has been suggested that even the 2,000 IU upper tolerable intake, the official safety limit, does not deliver the amounts of vitamin D that may be optimal.45
On a sunny summer day, total body sun exposure produces approximately 10,000 IU vitamin D per day. As a result, concerns about toxic overdose with dietary supplements that exceed 800 IU are poorly founded. It has been speculated that a person would have to consume almost 67 times more vitamin D than the current 600 IU recommended intake for older adults to experience symptoms of overdosage.45
Vieth believes people need 4,000–10,000 IU vitamin D daily and that toxic side effects are not a concern until a 40,000 IU/day dose.45
Other researchers agree with these findings. They suggest that older adults, sick adults, and “perhaps all adults” need 800–1,000 IU daily. They indicate that daily doses of 2,400 IU—four times the recommended intake—can be consumed safely.43
What conclusions do we draw from these findings, most importantly the demonstration of an association between vitamin D deficiency and the occurrence of various types of cancer? The most important take home message, especially for dermatologists, is that strict sun protection procedures to prevent skin cancer may induce the severe health risk of vitamin D deficiency. There is no doubt that UV radiation is mutagenic and is the main reason for the development of non-melanoma skin cancer. Therefore, excessive sun exposure has to be avoided, particularly burning in childhood. To reach this goal, the use of sunscreens as well as the wearing of protective clothes and glasses is absolutely important. Additionally, sun exposure around mid-day should be avoided during the summer in most latitudes. However, the dermatological community has to recognize that there is evidence that the protective effect of less intense solar radiation outweighs its mutagenic effect. In consequence, many lives could be prolonged through careful exposure to sunlight or more safely, vitamin D supplementation, especially in non-summer months. Therefore, recommendations of dermatologists on sun protection should be moderated.
As Michael Holick reported previously,46
we have learned that at most latitudes such as Boston, MA very short and limited solar exposure is sufficient to achieve “adequate” vitamin D levels. Exposure of the body in a bathing suit to one minimal erythemal dose (MED) of sunlight is equivalent to ingesting about 10,000 IU of vitamin D and it has been reported that exposure of less than 18% of the body surface (hands, arms and face) two to three times a week to a third to between a third and a half of an MED; (about 5 min for skin-type-2 adult in Boston at noon in July) in the spring, summer and autumn is more than adequate.46
Anyone intending to stay exposed to sunlight longer than recommended above should apply a sunscreen with a sufficient sun-protection factor to prevent sunburn and the damaging effects of excessive exposure to sunlight. Although further work is necessary to define the influence of vitamin D deficiency on the occurrence of melanoma and non-melanoma skin cancer, it is at present mandatory that especially dermatologists strengthen the importance of an adequate vitamin D status if sun exposure is seriously curtailed. It has to be emphasized that in groups that are at high risk of developing vitamin D deficiency (e.g., nursing-home residents; patients with skin type I or patients under immunosuppressive therapy that must be protected from sun exposure), vitamin D status should be monitored subsequently. Vitamin D deficiency should be treated, e.g., by giving vitamin D orally as recommended previously.46
It has been shown that a single dose of 50,000 IU vitamin D once a week for 8 weeks is efficient and safe to treat vitamin D deficiency.47
In a meta analysis of randomized controlled trials supplemental vitamin D in a dose of 700–1,000 IU prevented the risk of falling in older individuals by 19%.49
Another means of guaranteeing vitamin D sufficiency, especially in nursing-home residents, is to give 50,000 IU of vitamin D once a month. An alternative to prevent vitamin D deficiency would be the use of vitamin D containing ointments. However, it should be noted that vitamin D containing ointments are, at least in Europe, not allowed as cosmetics. These antiquated laws are the result of the fear of vitamin D intoxication that was evident in Europe in the 1950s48
and should be re-evaluated, for they do not reflect our present scientific knowledge. If we follow the guidelines discussed above carefully, they will ensure an adequate vitamin D status, thereby protecting us against adverse effects of strict sun protection recommendations. Most importantly, these measures will protect us sufficiently against the influence of vitamin D deficiency on the occurrence of various malignancies without increasing our risk to develop UV-induced skin cancer. To reach this goal it is of high importance that this information is transferred to every clinician, especially to dermatologists. Otherwise dermatologists will not be prepared for the moderation of sun protection recommendations, that is necessary to protect us against vitamin D deficiency, cancer and other diseases.