Lack of Sun Exposure & Type II Diabetes – Contemporary Evidence Suggests: There is a Link!

“No sun, no diabesity protection.” The evidence is equivocal and the number of studies low, but there is evidence that this statement could be true.

Ok, it’s November and not exactly sunny in the Northern hemisphere, but if you look back at the months June-August, how much sun exposure did you actually get, this year? Hardly any? Well, that’s bad news, because a recent review of the scant scientific evidence suggests that there is “a role of recreational sun exposure in reducing odds of T2DM incidence” (Shore-Lorenti. 2014).

In view of the fact that the contemporarily available evidence is not exactly comprehensive, you should yet consider the following overview of the potential effects and mechanism as a “work in progress”.

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As Shore-Lorenti et al. point out, the recent International Diabetes Federation (IDF) Diabetes Atlas (6th edition) describes a snapshot of the global diabetes burden in 2013 and projects this forward to the year 2035.1 Cur rently, an estimated 382 million global citizens have diabetes, costing around $1437 USD in 2013 for each person affected by the condition. Projections based on current trends predict that 592 million people will be living with diabetes by 2035; one in ten people will be affected, with an inordinate amount of fund ing required globally to treat diabetes and manage diabetic com plications ($627 billion USD in 2035).

And while scientists are feverishly searching for a solution for the diabesity epidemic, the ongoing research into the effectiveness of vitamin D supplementation in diabetes have yielded inconsistent results (Mitri. 2011). Against that background it appears almost negligent that only few scientists have yet taken a closer look at the factors that trigger vitamin D sufficiency or rather the global low vitamin D epidemia.

Lack of sun”low vitamin D” – that’s not all!

Figure 1: Australians who use sunscreen chronically have 50% reduced vitamin D levels (Matsuoka. 1988)

A lack of sufficient (unprotected) sun exposure – previous studies have shown that chronic sunscreen use decreases circulating concentrations of 25-hydroxyvitamin (Figure 1 | Matsuoka. 1988) – is one of the factors of which researchers speculate that it contributes to the development of vitamin D deficiency even in those of us who live in areas with a high annual sun-exposure.

Now, if restoring the 25-OHD (vitamin D) levels to normal does not work the anti-diabetic magic it is supposed to do and our D-levels are low due to insufficient sun-exposure, it appears only logical to assume that a lack sun-exposure and not a lack of vitamin D is one of the factors that contributes to the ever-increasing rates of diabesity – in conjunction with the usual subjects, obviously: The consumption of a junk-food diet and a lack of exercise, which is without doubt the #1 reason people in the Western Obesity Belt develop obesity, diabetes and the other characteristics of the metabolic syndrome.

Against that background it’s all the more surprising that evidence for an association between sun exposure and fasting serum glucose level is scarce.

“Typically, the lowest glucose levels occur during summer and levels peak in winter or early spring. One of these analyses [Shore-Lorenti et al. reviewed] went beyond simply observing trends in fasting glucose throughout the year: fasting plasma glucose was positively correlated with a measure of available sun and inversely correlated with temperature.” (Shore-Lorenti. 2014)

The study, the researchers from the University of Melbourne have in mind was conducted by Suarez, L. & Barrett-Connor, E. in 1988, already.
If you look at the data Suaraez & Barret-Connor generated, you can see – even without their statistical sophisticated analysis – that there is a significant correlation between possible sun exposure (Figure 1, left) and the fasting plasma glucose levels (Figure 1, right).

But sunlight gives you skin cancer, right? If you are the typical white-skinned tourist who grills in the sun for 8h a day in his 2-week beach holiday (=intermittent high exposure), yes! A chronic exposure to a moderate doses of sunlight, on the other hand, has been associated with a significant 27% reduced risk of melanoma (Nelemans. 1995).

Since physical activity may follow a similar circannual rhythm, it’s yet difficult to exclude that the effects Suarez & Barret-Connor observed were not corroborated (or corrupted?) by an increase in physical activity. However, Shore-Lorenti et al. believe that …

“[...c]onsidering that the unadjusted analyses and three of four of the studies included in the best evidence synthesis (including the study adjusting for physical activity) are in agreement, it is possible that future research may confirm that sun exposure reduces fasting glucose” (Shore-Lorenti. 2014).

Shore-Lorenti et al. also point out that the highest level of evidence (moderate) for an association between sun exposure and T2DM outcomes in adults originates from the study by Lindqvist et al. (2010). In their paper, the researchers from the Karolinska University Hospital report a reduction in odds of developing T2DM given increased recreational (rather than occupational) sun exposure. 

Figure 2: Leisure time sun exposure is associated with a significantly reduced risk (up to 50%!)
of developing T2DM in Swedish adults (Lindqvist. 2010)

In subjects with a low BMI the beneficial effect of using the tanning bed and sunbathing is even more pronounced (-60% risk). In the obese, however, it is significantly reduced (-10%) compared to the average reductions you see in Figure 2.

The fact that only leisure time, but not occupational sun exposure was linked to a significant reduced risk of developing type II diabetes may, as Shore-Lorenti et al. point out be due …

“[...] to the frequency of sun exposure (perhaps leading to tolerance), duration, intensity and site of exposure (sun protective clothing and behaviour differences between the two settings), or perhaps selection biases for such work (for example, fair-skinned people may avoid occupational sun exposure or a less healthy lifestyle may be associated with manual labour).”

Incidentally, a similar disparity between recreational and occupational sun exposure is well described for risk of developing melanoma (Chang. 2009).

A review by Chen et al. (2008) provides low-level evidence for an association between sun exposure and fasting insulin levels; fasting serum insulin was higher in summer than in winter. Overall, the results are yet inconclusive. A fact, Shore-Lorenti et al. ascribe to “the lack of adjustments made by the included study – particularly for BMI” (Shore-Lorenti. 2014)

Overall, we are thus left with the above overview (Table 1) as a conclusion of which the mere number of “unkown”s and “inconsistent”s tell you that we are not yet at the point to draw a water-proof conclusion.

Circadian Rhythmicity – Sunlight a La Carte: How to “Hack” Your Circadian Rhythm With 30min of Light Therapy Per Day | more

Bottom line: All in all, it appears to be likely that a lack of direct and regular moderate sun exposure is among the many lifestyle factors that increase your risk of developing type II diabetes.

The ameliorative effects of obesity, researchers like Lindqvist et al. (compare Figure 2) have observed, on the other hand, should remind you that you won’t get away with “just” getting enough sun exposure. Regular physical activity and a whole foods diet for obesity prevention are at least as important as the hours you spend in the sun | Comment on Facebook!

Speaking of hours in the sun, the overall beneficial effects are more likely to be related to the beneficial effects of sun exposure on circadian rhythmicity than on its effect on other chemical processes, such as the formation of vitamin D.


  • Chang, Yu-mei, et al. “Sun exposure and melanoma risk at different latitudes: a pooled analysis of 5700 cases and 7216 controls.” International journal of epidemiology (2009): dyp166. 
  • Chen, Shui-Hu, et al. “Community-based study on summer-winter difference in insulin resistance in Kin-Chen, Kinmen, Taiwan.” Journal of the Chinese Medical Association 71.12 (2008): 619-627.
  • Lindqvist, Pelle G., Håkan Olsson, and Mona Landin-Olsson. “Are active sun exposure habits related to lowering risk of type 2 diabetes mellitus in women, a prospective cohort study?.” Diabetes research and clinical practice 90.1 (2010): 109-114.
  • Mitri, J., M. D. Muraru, and A. G. Pittas. “Vitamin D and type 2 diabetes: a systematic review.” European Journal of Clinical Nutrition 65.9 (2011): 1005-1015.
  • Nelemans, P. J., et al. “An addition to the controversy on sunlight exposure and melanoma risk: a meta-analytical approach.” Journal of clinical epidemiology 48.11 (1995): 1331-1342.
  • Shore‐Lorenti, Catherine, et al. “Shining the Light on Sunshine: a systematic review of the influence of sun exposure on type 2 diabetes mellitus‐related outcomes.” Clinical endocrinology (2014).
  • Suarez, L., and E. Barrett-Connor. “Seasonal variation in fasting plasma glucose levels in man.” Diabetologia 22.4 (1982): 250-253. 

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8 Holiday Fitness Tips

Don't let the holidays derail your gains. Make time for friends, family, AND fitness with these tips!

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Clutch Nutrition For High-Intensity Training

Sprints, jumps, and agility work can work wonders for body composition. But to get maximum results from your high-intensity efforts, back them up with smart nutrition and supplementation. Here's how!

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How To Press 200 Pounds Overhead

Somewhere along the line, you stopped believing that you could push heavy weights over your head. It's time to rebuild your strict press and aim for the skies!

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7 Ways To Build Your Biceps Peak!

Is your biceps peak looking more like a molehill than a mountain? Jack up your arms with these 7 peak-performance strategies!

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The Acute & 24h Effects of 3 Types of High Intensity Circuit Training on Testosterone & Cortisol in Young Trained Men.

It’s obviously to have the 24h effects on testosterone and cortisol than only those measured after the workout , but can we make solid conclusions based on the additional data?

In spite of the fact that the acute testosterone and cortisol response to exercise appears to have little direct effects on the overall training outcome (Schoenfeld. 2013), acute increase in cortisol and reductions in testosterone, i.e. a decrease in the testosterone:cortisol ratio is a classic feature of overtraining and can very well blunt, if not reverse the beneficial effects of exercise on your health and body composition.

Against that background a recent experiment that was conducted by researchers from the University of Chieti-Pescara in Italy could be of great interest to everyone who is performing high intensity interval training on a regular basis. Why?

Well, in contrast to previous studies, Blasio et al. investigated both the acute and 24h effects of a high intensity interval resistance training regimen in trained young men.
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To characterize the effects on heart rate and hormonal responses the subjects, eight trained, healthy trained men (28.61 ±3.51 yrs), performed three different workouts which had the same exercises, the same load and number of repetitions for each exercise, but different exercise order, recovery and speed of execution.

  • RANDOM workout: the assigned goal was to complete the assigned repetitions respecting only two duties. The first one was don’t stop until all of the repetitions were completed; the second was that there were no assigned order of execution of exercises and no assigned consecutive repetitions to complete.

    Participants were thus free to choose both the order of exercises and number of consecutive repetitions for each exercise (i.e. 2 repetitions of kettlebell swing, 10 repetitions of medicine ball slam, 20 repetitions of squat, 4 repetitions of spin with Bulgarian bag, etc.).

    No recovery period was assigned, except the time necessary to move from a station to another, and no speed of execution of exercises was assigned: participants were free to choose the preferred speed. 

  • LADDER workout: respecting the following order of execution, kettlebell swing, medicine ball slam, spin with Bulgarian bag, squat, pull-up, burpee, participants had to complete the total repetitions according to a pyramidal scheme (e.g. 1st lap 10 repetitions at each exercise, 2nd lap 9 repetitions at each exercise) until the total number of repetitions of each exercise was executed.

    Each lap of the circuit was followed by 1 minute of recovery. No speed of execution of exercises was assigned: participants were free to choose the preferred speed. 

  • AS SOON AS POSSIBLE (ASAP) workout : respecting the following order of execution, kettlebel swing, medicine ball slam, spin with Bulgarian bag, squat, pull-up, burpee, participants had to complete the total volume in six laps executed as soon as possible.

    During each lap participants had to complete the sixth part of total number of repetitions of each exercise without rest among exercises. Each lap of the circuit was followed by 1 minute of recovery.

Salivary samples were collected before and after each workout, at 11:00 p.m. and at 7:00 a.m. of the following day. Salive was also collected during a non-training day. Similarly, before and after the workout, plasma lactate was measured while a beat-to-beat heart rate recording was executed during each workout. Cortisol (C) and testosterone (T) were measured in salivary samples.

2h before the workouts the subjects who had to abstain from sexual intercourse, stimulants and alcohol from 2 days before to the experimental days and until 9:00 a.m. of the following day, consumed a standardized meal that was lower to 400 and consisted of 33 cl of water, 35 cl of orange juice and two 30 g energy bars (Power Sport Double Use, Enervit, Milan, Italy).

Let’s look at the results

While the protocols elicited the same heart rate response (the major part of each workout was spent between 80 and 100% of maximal heart rate, confirming the high cardiovascular intensity of the workouts), they elicited different hormonal and lactate variations with the LADDER workout producing the lowest lactate increase and the RANDOM workout eliciting the highest lactate, cortisol and testosterone increases.

Figure 1: Relative changes in hormone and lactate concentration in response to the workouts (Di Blasio. 2014)

When C was considered in ratio with T no significant differences have been shown among workouts-induced variations. Results of the analysis of covariance, executed on significantly modified variables, confirmed that basal hormonal and lactate values did not influence their variations.

When they studied the effects of workouts on prolonged hormones production (i.e. until the morning following the morning, di Blasio et. al. found that observed that observed that

“C had both time (F=179.723; p < 0.001) and group × time effect (F=10.942; p < 0.001): while during non-training day there is a physiological decline of C production at 11:00 p.m., during training days its decline is not present but seems to have a continuous increase from 7:00 p.m. to 7:00 a.m.” (Di Blasio. 2014)

For the testosterone production the authors found both time (F=443.340; p < 0.001) and group × time effect (F=3.254; p=0.008) even if the group × time effect seems determined by the samples collected at 7:00 p.m., so that the effects cannot be ascribed fully / exclusively to the workout.

Figure 2: 23h hormone profile after the RANDOM, LADDER, ASAP workouts on a control day (di Blasio. 2014)

What is most interesting, though, is the cortisol to testosterone ratio. It shows the greatest inter-group differences and could potentially be of great physiological relevance (Crowley. 1996). In that, the LADDER workout has the most negative effect, as it will totally blunt the natural decline of the C:T ratio at noon.

In case you’re planning to incorporate circuit training into your schedule, make sure to have a huge chunk of beef after your workouts ;-) – “Post-Workout Steak “Supplementation” (135g of Lean Beef) Augments Improvements in Body Composition In Response to 8 Weeks of Circuit Resistance Training” | more

Bottom line: As usual, it is difficult to interpret the results in order to make concrete practical recommendations. The lactate and hormonal data does yet suggest that the “random” order, i.e. a training that involves a self-selected exercise order and rep speed, as well as little to no rest between exercises is the least, the ladder training, with its decreasing 10, 9, … rep numbers and one minute rest between each lap of the curcuits is the most metabolically demanding workout.

Whether and to which extend this translates into an increased risk of overtraining, let alone increased muscle and strength gains, on the other hand, remains to be seen. In view of the overall effect on lactate levels and the C:T ratio, though, the study does suggest that you better be careful with high intensity circuit / interval resistance training sessions and give your body adequate time to rest and recover | Comment on Facebook!


  • Crowley, Michael A., and Kathleen S. Matt. “Hormonal regulation of skeletal muscle hypertrophy in rats: the testosterone to cortisol ratio.” European journal of applied physiology and occupational physiology 73.1-2 (1996): 66-72. 
  • Schoenfeld, Brad J. “Postexercise hypertrophic adaptations: a reexamination of the hormone hypothesis and its applicability to resistance training program design.” The Journal of Strength & Conditioning Research 27.6 (2013): 1720-1730.

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Winning Healthy Recipe Of The #FitMenCookoff

The dishes have been reviewed and the delicious, healthy meals have been considered. The top finalists have been narrowed down to one all-star dish. Here's the winner of the #FitMenCookoff!

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