Is early morning sunlight as good as evening sunlight for health?

Question

There are several references which say that early morning sunlight would give the best benefits (like this and that). This comes from the common consensus that most of the harmful rays, at that time, are filtered out by a thicker portion of the atmosphere through which the light of the sun must pass through to reach our skin.

Doesn't this theory equally apply to evening sunlight as well. Are there any (notable) differences in the health benefit that one might receive from the early morning sunlight from that of the evening sunlight.

Answer 1

Actually, I am a frequent flyer (I think I spend at least 10% of my year in an airplane or an airport) and I discussed the problem of sunlight with my treating physician.

First, sunlight has an impact on the circadian rythm (which involves the secretion of melatonin, cortisol, control of body temperature) which regulates your wake/sleep cycle.

The effect of evening light was examined in a study where a subject was exposed to several hours of light every evening for a week, and the timing of the rhythms of core body temperature and plasma cortisol were measured.

The authors reported that

Both rhythms were shifted by approximately 6 hours, and examination of temperature data collected throughout the experiment suggested that the shift had already occurred after only 2 days.

Dysregulated circadian rythms (due to impaired melatonin, cortisol and body temperature levels) is associated with many diseases among which psychiatric diseases and metabolic syndrome.

So, this possibly explains the results found in the study you linked on the telegraph.co.uk suggesting that early sunlight might reduce the risk of developing metabolic syndrome, probably because this is associated with a physiological (ie normal) circadian rythm.

Finally, you linked one study regarding "sunbathing is good for you". I think, this should be taken with caution, particularly because increased sunbathing is linked to skin cancer.

We also discussed the effect of different timing of the day to produce the maximum of Vitamin D (I am already deficient...). He mailed me following extracts from this review

Factors that affect cutaneous production of vitamin D3 include latitude, season, time of day, air pollution, cloud cover, melanin content of the skin, use of sunblock, age and the extent of clothing covering the body. When the sun is low on the horizon, the atmospheric ozone, clouds and particulate air pollution absorb UVB radiation, limiting the amount that reach the surface of the Earth. The zenith angle of the sun plays a critical role in vitamin D3 production. When the zenith angle is more oblique, the path length through the stratospheric ozone layer is increased and hence, fewer UVB photons are able to reach the earth’s surface.

So overall, current research evidence speaks in favor of morning sunlight. Evening sunlight might on the contrary be associated with negative effects.

Hope this helps!

Answer 2

It is true that there are many benefits from morning sunlight. It helps people who are suffering from vitiligo and white patches. The morning sunlight gives Vitamin D which is good for our body and also for our bones, But there is a specific time in which you have to get exposed to sun and the time is from 7am - 9am. And there is no benefits of evening sunlight.