Even if this does not exert any noticeable effects now, the situation may be different by the time they reach even just 40-50 years of age.

A decade ago, the Estonian Defense Forces (EDF) inquired whether the health of young men of conscription age, meaning 18 and over, might be objectively assessed, and how the military might helped to improve their health and quality of life during the conscription term itself – typically around a year in duration.

This idea was the germ which led to a doctoral thesis defended by orthopaedist Leho Rips.

Rips was particularly interested in the volumes of Vitamin D in conscripts' bodies, and impacts on their physical performance.

In order to explore this, Rips mapped the health status and physical parameters of young men entering conscription in the years 2015 and 2016. In short, he sought to understand how the health of young men changes both over the short term and during intensive, boot camp-style training periods. The men were generally aged between 18 and 25. Rips was surprised to find that young men suffered from significant Vitamin D deficiency.

The optimum level of Vitamin D has been debated in the scientific community. There are different approaches, but two thresholds are commonly used: Either 50 or 75 nanomoles per liter (nmol/L). Rips' research was based on the idea that an optimal year-round Vitamin D level comes to 75 nmol/L.

The first study followed young men who had commenced their conscription terms in mid-summer. As early on as July, 77 percent of the subjects had a Vitamin D deficiency is deploying the 75 nmol/L methodology. However, when using the 50 nmol/L basis instead, the situation was practically the reverse: 75 percent of the young men entering conscription had adequate Vitamin D levels, that July.

But even then, a quarter of the total still fell below the threshold, which came as a significant surprise to Rips.

He said: "These are young men we're talking about. We would therefore assume they are physically active, energetic, go outside, run around, take their shirts off, and get some sun exposure," referring to one source of Vitamin D.

"Summer was already underway, so we assumed that the guys had been outdoors," said Rips.

Importance of Vitamin D supplements

Since the initial study already revealed significant Vitamin D deficiency even in summer, this finding formed the impetus for further research.

"The preconception that Vitamin D levels are fine in summer as the sun is shining and so no Vitamin D supplementation is needed was false, it turned out."

With the further studies, the conscripts were divided into several groups. One group consisted of a control group, which was monitored only and received no extra Vitamin D / was not deprived of any Vitamin D.

In the other groups, the young men were administered varying doses of Vitamin D, to test the effects of same.

When the first group of young men was reexamined in spring, none of them were found to have the recommended 75 nmol/L Vitamin D level in their bloodstream, and only 8 percent displayed levels above the secondary baseline noted above, of 50 nmol/L.

Put simply, by the following spring, 92 percent of the subjects were suffering from Vitamin D deficiency.

That they were still functioning Rips put down to the immune system being able to operate fully at 75 units, while the body can still manage reasonably well at 50 units.

However, when the level falls below 50 units, the body begins to limit bone formation.

A critical deficiency is defined as a Vitamin D level below 25 units, meaning to all intents and purposes, the body is virtually depleted of Vitamin D.

While 2 percent of the young men had a deficiency that severe when tested in the July, the figure rose to 36 percent, ie. rose 18-fold, by the following spring and after the dark winter months.

"We're talking about conditions which determine the functioning of our immune system and bone quality," Rips said.

Opinions differ within the medical community on the effects of Vitamin D deficiency.

The consensus is that a deficit may increase the risk of depression, and this has also been linked to an elevated risk of diabetes and many other diseases.

Collating all the negative effects with the scope of a year-long study was not viable, however.

Long-term impacts and osteoporosis risks

As Rips put it: "When someone learns now that they have a Vitamin D deficiency, then takes supplements for a month and goes off to Tenerife in the spring thinking all is well, well unfortunately, that is not the case," since temporary rises in Vitamin D intake don't affect bone quality in the long term, and bone thinning can still occur.

"It's a continuous process, plus the individual won't perceive any change," he said.

With that a subject may only get a grasp of the effects of an earlier Vitamin D deficiency in older age, once the unexpected fractures happen, or when diabetes gradually develops.

According to Rips, the conscripts covered in his studies will likely only feel the negative effects of Vitamin D deficiency once they are in their forties.

For most of the populace, Vitamin D levels fluctuate throughout the year; they are slightly higher in summer, and very low in spring.

"I jokingly refer to Vitamin D as a retirement 'pillar,'" Rips said, referencing the three pillars of the Estonian pension system.

"Taking Vitamin D won't provide any immediately visible results. However, if you've been taking it consistently throughout your life chances are your overall health indicators and bone quality will be much better, when compared with those of your peers," he explained.

The dosage and frequency of Vitamin D supplements is also a hotly debated topic as, according to Rips, outdated information sometimes does the rounds.

The issue often lies in discussing dosages that apply to other regions of the world.

Generally, recommendations for Estonians can best be based on studies conducted locally, as they naturally account for the country's specific characteristics in geography, climate, genetics, society and so on.

For example, Vitamin D-fortified products are very common in the Nordic countries.

Dietary and supplement best practices for Vitamin D

Among other things, Vitamin D gets added to various dairy products in these cases, to apparent good effect.

"With Norway, it's clear how these foodstuffs significantly help maintain the general population's Vitamin D levels," Rips said.

However, in Estonia, consumption of dairy tends to be quite modest despite the range of products available.

While the above research focused on young men, Rips believes that women may exhibit even lower levels of Vitamin D residual in their bodies.

The reasons for this are not primarily due to diet, he said. "This is mainly because young men still tend to take their shirts off. But there's a widespread misconception that being outside for 15 minutes with just your hands exposed to the sunlight is enough. In reality, that's not enough. You need to spend hours outside, with at least half your body exposed to the sun, to synthesize sufficient Vitamin D," he said.

While it was the case that a few subjects in the study, who were visibly tanned and so likely spent a lot of time outdoors ahead of the study, achieved natural summer Vitamin D levels as high as 150–185 nmol/L.

On the other hand: "Unfortunately, it seems that the majority of young men sit at their computers during the summer and don't get out in the sun."

As well as low Vitamin D levels, it is likely that young women also experience iron deficiency more frequently than the guys, he added.

"I don't see much of this any more, but the younger colleagues I'm currently teaching, who will still be working in about 20 years' time, are likely to see more young people presenting with osteoporosis, and a heightened risk of fractures."

Safe dosages and future health risks

"What we currently consider retirement-age fractures will, in the future, occur in pre-retirement individuals. I think this timeline will shift forward by 10–15 years," Rips added.

Osteoporosis, a thinning of the bones, is a condition characterized by a decrease in bone density.

Bone strength also depends on calcium content, and the calcium needed by the body is primarily obtained from dairy products.

Calcium content in the bones decreases in cases of osteoporosis, making the bones brittle, and causing them to lose elasticity (bone plasticity), resulting in a loss of normal strength, which in turn also increases the risk of fractures.

At the same time, it is often said that grandma didn't take Vitamin D supplements and yet lived to a ripe old age.

The solution to this has been mentioned already: "In the past, the grandparents worked outside until dark and went out at sunrise, all year round," Rips said.

"Present-day Estonians' forefathers' diets were likely much better and of a higher quality, with a greater proportion of natural foods included, compared with today. So in addition to the outdoor lifestyle they obtained significantly more Vitamin D from their food than we do today. Modern-day young people prefer different menus than fresh fish and dairy products however," Rips explained.

Ultimately while nutrition is important, the average Estonian obtains less than 10 percent of their required Vitamin D from what they eat, making it difficult to compensate for a deficiency solely through diet.

In the second part of the study, Rips examined whether Vitamin D supplementation affects physical performance. In short, it had no discernible effect, he found.

This has also been demonstrated by most studies conducted worldwide.

"We only observed that during the military training process, physical test results improved. However, this was due to the training, not the Vitamin D," he continued.

Vitamin D dosage guidelines and risks of overdose

Nonetheless, looking at young men's physical performance over the past decade brings little cause for optimism.

"The reality is sadly a grim one."

In fact: "Testing standards were adjusted just so that the boys could somehow pass," he revealed.

The physical capabilities of young people have regressed significantly over the past decade.

If a person starts at 18-20 years of age, they can certainly build bone mass. "However, if movement habits and an awareness of the importance of physical fitness awareness haven't developed by then, awakening to these issues later in life often comes too late to do much about it," he said.

Vitamin D is inherently fat-soluble and functions similarly to a hormone.

"When it comes to Vitamin D in tablet form, it doesn't get absorbed adequately. These also contain additional fillers that the human body doesn't need," Rips said.

How much Vitamin D should you take?

Pharmacy shelves brim with products containing 400-4000 units of Vitamin D.

"Our study confirmed that the safe limit for Vitamin D supplementation is 4,000 units per day," said Rips. "If a person is afraid that they may overdose, they can also limit themselves to 2,000 units, which is considered the golden mean at the moment. Our studies also show that the risk of overdose is low, at least among active young men," he added.

Many international recommendations say that 600 units should be consumed. However: "According to our research, this has no effect at all, but rather the vitamin D content drops and this amount does not even maintain the level that a person had before."

To reiterate: If an individual does not have the opportunity to determine their vitamin D levels, they can safely take 1,200-2,000 units of vitamin D. However, if they are significantly deficient, 4,000 units will more likely help increase their vitamin D levels.

It is also possible to get too much Vitamin D.

The level of toxicity in the bloodstream in this case is 750 nanomoles per liter, Rips said. But to reach that: "This toxicity is reached when you take half a pot of 4,000-unit capsules, every day."

"In the experiment, even young men who took 4,000 units did not achieve blood levels higher than 130 nmol/l as of the spring. This is not even close to the toxic levels. So our study reiterated what was previously known: The safe limit for vitamin D supplementation is 4,000 units per day," Rips concluded.

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