Sunlight provides more than just a pleasant way to start the day; it has certain distinct health benefits. Most notably, sun exposure stimulates the production of vitamin D — a crucial nutrient for the overall health of our bodies. An estimated 40% of Americans are vitamin D-deficient for at least part of the year, and vitamin D is most effectively absorbed if it is obtained from a short bout (probably less than 10 minutes per day for most people) of sunshine several times per week. And while that exposure needs to be balanced with the skin cancer risks it poses, many leading clinicians nevertheless continue to recommend a little sun. Whether that’s best obtained in the morning or mid-day (when some scientists believe the yield of vitamin D is highest, without as high an increase in risk of cancer) remains a topic of debate in research circles. Certain sun in the morning benefits unrelated to vitamin D are frankly less significant, clinically — and yet they could be meaningful to particular individuals, for whom sun exposure in the morning hours may notably boost mood, cognition and sleep health. 

The benefits of sunlight in the morning

Vitamin D

While there are potential benefits to mood and sleep quality, by far the most significant benefit to getting sunlight in the morning (or any other time) is that it remains the best way to obtain enough vitamin D. 

To quote Mayo Clinic, “vitamin D is a nutrient your body needs for building and maintaining healthy bones. That's because your body can only absorb calcium, the primary component of bone, when vitamin D is present. Vitamin D also regulates many other cellular functions in your body. Its anti-inflammatory, antioxidant and neuroprotective properties support immune health, muscle function and brain cell activity.”

More than one billion children and adults worldwide are deficient in vitamin D. Children who don't get enough vitamin D may not grow as much as others their age. (They also have a chance of getting a rare disease called rickets, which causes weak bones.) Adults are at increased risk of developing osteoporosis, putting them at significant risk of fractures and other bone-related ailments, as well as increased dental carries. 

But beyond bone-related disorders, vitamin D deficiency may put you at increased risks for a host of other medical disorders. Scientific research cannot always demonstrate proof of cause-and-effect with vitamin D, but that’s in part because, like with many other micronutrients, vitamin D is a necessary but not sufficient factor for key cell-biologic processes. As one scientist explains, “vitamin D is an enabler; it must be present for those processes to occur, but it does not, itself, stimulate or cause them.” Nonetheless, vitamin D deficiency has been linked to: 

Cardiovascular disease (CVD)
Colon and other cancers, especially in women

Type 2 diabetes
Diabetic peripheral neuropathy

Inflammatory bowel disease (IBD) and other diseases of the gastrointestinal tract

Preeclampsia and preterm birth
Polycystic ovary syndrome (POCS)
Autoimmune disorders
Infectious diseases

Neurological/vascular disorders

Other sunlight benefits

Vitamin D production is not the only physiological response stimulated by sunlight. Others include:

• Release of nitric oxide (NO): Stimulated by UVA radiation, NO in turn stimulates vasodilation and lowering of blood pressure. (See our report. Exploring the benefits of heat exposure, for further details on NO on how heat therapies can stimulate this important signaling molecule.) In a 2012 study, during active exposure to UVA, diastolic blood pressure declined by roughly 5 mmHg and remained lower for 30 minutes after exposure. Lower blood pressure is associated with reduced risks for stroke and coronary heart disease.
  
• Beta-endorphin production: Research has shown that exposure to UVB sunlight aids the production of beta-endorphins, hormones associated with boosting mood, promoting relaxation, boosting the immune system, and promoting wound healing and cellular differentiation. Sun exposure can be a natural remedy for those struggling with low mood or seasonal affective disorder (SAD), a type of depression that occurs during specific seasons, typically in the winter months.
  
• Regulation of circadian rhythm: Exposure to light of most kinds, during daylight hours, is known to regulate your internal body clock, or circadian rhythm. The natural light signals to the brain that it's time to be awake and be alert, helping us feel more energized during the day but also more ready for darkness at night when we can associate the latter with sleep time (and thus improve sleep onset and sleep duration). Thus, daytime light exposure can improve symptoms of insomnia in certain individuals.
  
• Enhanced cognitive function: From improving reaction times to boosting attention span, sunlight exposure has been linked to enhanced cognitive function. This has been attributed to the combined effects of improved sleep patterns and increased serotonin production.

What the sun (and vitamin D) haven’t proven they can do

As mentioned previously, a lack of sun exposure, and in particular vitamin D deficiency, has been linked to many disorders, including those we listed above. But to reiterate, associations don’t mean cause, and sun and vitamin D may not directly prevent or cure most of these disorders. In some of these cases, adequate vitamin D levels might contribute to reduced risks of disease onset. However, this does not necessarily mean that vitamin D intake in an existing disease state will have a clinically significant impact upon disease management (i.e., amelioration of symptoms or disease progression). In other words, vitamin D is often touted for many benefits without sufficient clinical evidence. For many disease states, observational studies of D’s impact may have been conducted, but such studies are not as compelling as randomized controlled clinical trials. 

The same goes for studies of sun exposure: in observational studies, there are often confounding variables. For example, there may be other reasons that less sun correlates with certain diseases. People may not be going outdoors because they are ill or less inclined to exercise. Or a low vitamin D blood level could be a consequence of obesity; (the vitamin is soluble in fat, so it can become sequestered inside adipose tissue), meaning that the detriment to health may not be from low vitamin D directly, but from excess body weight, too little physical activity or other known influences on a person’s health.

Here are just a few examples of what vitamin D has not proven it can do:

• While vitamin D deficiency correlated with higher risks of colorectal cancer in a large study, in other studies the results have been mixed, as has been the case in studies of vitamin D’s impact upon many other cancers.
  
• Clinical trials show that vitamin D supplementation does not reduce CVD risk.
• Clinical trials to date provide little evidence that vitamin D supplementation helps maintain glucose homeostasis, reduces the risk of progression from prediabetes to type 2 diabetes, or helps manage the disease, particularly in vitamin D-replete individuals.
• Clinical trials did not find that vitamin D supplements helped prevent or treat depressive symptoms or mild depression, especially in middle-aged to older adults who were not taking prescription antidepressants. (No studies have evaluated whether vitamin D supplements may benefit individuals under medical care for clinical depression who have low or deficient 25(OH)D levels and are taking antidepressant medication.)
• Experts have reached no firm consensus on whether vitamin D can help prevent multiple sclerosis (MS), given the lack of clinical trial evidence.
• In a randomized clinical trial that involved hospitalized patients with moderate to severe COVID-19, a single high dose of vitamin D did not [our emphasis] significantly reduce hospital length of stay, as reported in a 2021 JAMA paper.
• In IBD (an umbrella disease state which includes Crohn’s disease, or CD, and ulcerative colitis, or UC), while several controlled clinical trials have found that vitamin D helps to prevent relapse and lower activity scores, a 2021 review cautions that “it remains to be established whether and at which doses these local effects of vitamin supplementation on the gut microbiome will translate into host health benefits.” Put bluntly, it’s unlikely that vitamin D is a cure for IBD.

We need to realize that vitamin D may not be “a magic bullet.” For bone health, it probably is. For other disease states, it may play a beneficial role, but it is likely far from a major player. Saying that does not mean that you don’t need vitamin D; you absolutely do. And sun exposure may be the best method of getting it.

Is morning sun exposure the most advantageous?

Our frank conclusion based on research to date: The time that you go outside for brief exposure to sunlight is not of huge clinical significance. It’s more important that you just get out, every other day, for about 10 minutes without being completely covered up. And if you cannot, you should have a discussion with your medical provider about the possibility of initiating vitamin D supplementation. 

Morning sunlight: Potential advantages 

Morning sun benefits might prove advantageous for certain individuals, but not for all. Like numerous physiological processes, how sunlight timing affects us appears to be highly individualized.  

• For those individuals that experience insomnia, morning sun could prove advantageous, as it aligns well with beneficial circadian rhythms. 
• Cognitive functioning may also be enhanced by morning sunlight, as it gives an endorphin boost just prior to the longest part of your workday, assuming your work hours approximate a common 9-5 timeframe.
• For those that tend to lose track of time, morning sun rays are less intense, so if by mistake you stay out too long, you’ll have less of a tendency to burn.

Mid-day sunlight: Potential advantages

• Better vitamin D production at lower cancer risk: Contrary to what you might at first presume, a 2008 study, and others like it, have determined that noon is the best time to get an optimal vitamin D supplement from the sun at minimal risk of getting cutaneous malignant melanoma (CMM). The science around this is complex and has to do with the relative lengths of UVA vs. UVB wavelengths at various times of day, and factors such as degree of scattering of solar radiation and wavelength “fluence rates.” The determination: shorter sun exposures around noon are preferable, giving a maximum yield of vitamin D to a minimal risk of CMM, versus longer exposures in the early morning or afternoon lengths.‍
• Mid-day sun exposure may actually build up protective pigments that can protect you from damaging UVA rays. According to a 2015 review, mid-day (but note: this is a wide timeframe of 10 a.m. to 3 p.m.) is actually the best time to promote “the thickening of the stratum corneum (the outermost layer of the epidermis) and increased skin pigmentation through production of melanin.” This paired response actually protects the skin and deeper tissues from the deeper penetrating and damaging UVA rays while retaining benefits (e.g., vitamin D stimulation) from UVB exposure.

There’s no one-size-fits-all sun prescription

Whether it’s duration or time of day, bear in mind that clinicians have not formed any one consensus recommendation for sun exposure, in part because the amount of sunshine needed is different among individuals. Factors affecting sunshine exposure and absorption include skin complexion, clothing, sunscreen used, location, time of year, time of day, and cloud cover. In general, the lighter your skin and the closer you are to the equator, the faster you make vitamin D.

Current (but very general) advice is for people to stay in the sun for half as long as it takes their particular skin type to burn before covering up and retiring to the shade. This should give them all the vitamin D they need without increasing the risk of skin cancer.

Do note that sitting by a window doesn’t work for UVB light. You can only stimulate vitamin D production by going outside. 

What to do when you can’t get out in the sun

If your doctor suspects you're not getting enough vitamin D, a simple blood test can check the levels of this vitamin in your blood.

If you are deficient, but cannot increase your sun exposure (perhaps because you are elderly or have a condition which affects your ability to absorb vitamin D), a combination of vitamin D-rich foods and a vitamin D supplement may be well worth considering. We cite “both foods plus a supplement” because, frankly, Vitamin D isn't naturally found in many foods — although you can get it from fortified milk (and some brands of yogurt) or orange juice, fortified cereal, fatty fish (such as salmon, mackerel and sardines), and fish liver oils. Small amounts of D are found in eggs, beef liver, mushrooms, and certain cheeses.

In the U.S., the recommended daily intake of vitamin D from food or supplements is as follows:

• Infants up to age 12 months: 400 international units (IU) or 10 micrograms (mcg)
• Children and teenagers: 600 IU or 15 mcg
• Adults up to the age of 70 years old: 600 IU or 15 mcg
• Adults aged 71 years old and over: 800 IU or 20 mcg
• During pregnancy and breastfeeding: 600 IU or 15 mcg

Vitamin D supplementation

If your medical provider determines you are deficient in D and unable to increase it naturally (via foods/sun), taking a supplement will likely be recommended. 

Bear in mind that excess amounts of vitamin D are toxic. Because vitamin D increases calcium absorption in the gastrointestinal tract, vitamin D toxicity results in marked hypercalcemia, which in turn can lead to nausea, vomiting, muscle weakness, neuropsychiatric disturbances, pain, loss of appetite, dehydration, polyuria, excessive thirst, and kidney stones. In extreme cases, vitamin D toxicity causes renal failure, calcification of soft tissues throughout the body (including in coronary vessels and heart valves), cardiac arrhythmias, and even death. 

Fortunately, experts do not believe that excessive sun exposure results in vitamin D toxicity.

Key takeaways

So, what are the sun in the morning benefits? Moderate sun exposure (less than the time required to burn) to the arms, shoulders, trunk, and legs has health benefits, particularly the natural stimulation of vitamin D and, of lesser significance, several other physiological responses. On balance, and if great care is taken to minimize the sun exposure, these benefits appear to outweigh the risk of skin cancer from sunlight. After a minimal exposure, which varies by individual and circumstance, of just minutes every other day, covering the skin or seeking shade is recommended. Some experts opine that mid-day sun, near noon, may be the most beneficial, but morning sun may be preferable for individuals with sleep or mood issues. If you are unable to get outside, even briefly, for days at a time, most clinicians recommend you get tested for vitamin D deficiency and consider taking a supplement.