Vitamin D

For the past several years the data in support of increasing vitamin D intake for every living human has been mounting. This week the American Journal of Clinical Nutrition features a collection of new research articles addressing the trends in vitamin D status and optimal dose recommendations.

This week’s take home lesson: While current research indicates we should be getting more vitamin D than is presently recommended, as a whole our vitamin D levels appear to have decreased in the past 15 years. The best way to combat this deficiency is with vitamin D supplements.

Vitamin D is a fat-soluble prohormone and essential nutrient produced when ultraviolet radiation (UVB) contacts our skin. It is probably best known for its role in bone metabolism (it has been shown to be more important than calcium for maintaining bone health), however recent studies indicate that vitamin D is essential for other physiological process as well.

Low blood levels of vitamin D have now been associated with many different chronic diseases including cancer, coronary heart disease, multiple sclerosis, Alzheimer’s disease, tuberculosis, depression, hypertension, periodontal disease, schizophrenia, seasonal affective disorder and type 1 diabetes.

In light of these findings, many nutrition researchers have argued for increasing recommended levels of vitamin D intake, but making population-wide recommendations have proved difficult for world health agencies because of large variability and uncertainty in vitamin D requirements.

There are several things to consider when evaluating vitamin D status in an individual. Latitude (sun exposure) is probably the single best predictor of vitamin D status. Anyone living in San Francisco or further north cannot get enough sun exposure to achieve sufficient vitamin D status, particularly during the winter months.

Because vitamin D is fat-soluble, it is retained in body tissues for several months after sun exposure. For this reason, people living at far north latitudes are particularly vulnerable to vitamin D deficiency because they frequently do not store up sufficient vitamin D during the summer to sustain their needs during the winter.

To further complicate matters, it is incredibly difficult to obtain vitamin D through dietary sources. Fatty fish and eggs are the only natural sources of vitamin D, though they are probably insufficient to achieve optimal status. Milk and soy products are typically fortified with vitamin D, as are some juices.

Skin pigmentation, sun avoidance and body composition (high body fat) are all associated with vitamin D deficiency. Darker skin tones do not convert sunlight to vitamin D as easily as lighter skin tones. Sunscreen blocks virtually all vitamin D synthesis. Body fat reduces bioavailability of vitamin D tissue stores.

This week’s study by Anne Looker et al, suggests that increased body mass as well as awareness of skin cancer risk and use of sunscreen have contributed to a significant decline in vitamin D levels in north America in the past decade.

The good news is that supplementation does appear to be effective at improving vitamin D status. Though there is still some disagreement on what the optimum blood levels of vitamin D are, it is generally agreed that they are much higher than currently recommended by any world health organization. One of the principle motivations of the present studies is to inform new vitamin D recommendations.

Kevin Cashman et al offers estimations of dietary requirements of vitamin D for healthy adults. They performed a randomized, placebo-controlled study testing the effects of different vitamin D doses and how they effect blood vitamin D levels.

The absolute minimum amount of vitamin D supplementation recommended by the study is 8.7 ug/day, or approximately 400 IU. This was to maintain blood serum levels greater than 25 nmol/L, and is double the current FDA recommendation for people under age 50. However, this suggestion is only sufficient to avoid deficiencies associated with bone loss and not other chronic diseases.

“The data from the present study clearly show that vitamin D tissue stores, developed during summer via exposure of skin to sunshine, were not sufficient to maintain serum 25(OH)D concentrations of greater than 25 nmol/L in most of the population [during winter], and that dietary vitamin D is an absolute requirement to maintain status above this minimum threshold.”

But the recommendations do not stop here. To maintain blood serum levels of greater than 50 nmol/L–a range more consistent with lowering risk of chronic disease–the study recommends 28 ug/day or 1100 IU of vitamin D. To keep blood serum above 80 nmol/L (from all I have read this is what I would recommend), 41 ug/day or 1650 IU is needed.

Remember this is most important if you are overweight, live north of San Francisco, get little sun exposure or have darker skin. Very rarely do I recommend vitamin supplements (they are not usually effective and are sometimes dangerous), but in this case the evidence is unequivocal.

Vitamin D supplements are easier to find than in the past, but they are usually packaged with calcium and are insufficient in dosage. Men should be wary of excess calcium supplementation since it is associated with an increased risk of prostate cancer.

I will continue looking for a good vitamin D supplement and will post when I find one I am happy with. If you have any recommendations, please share them with us.

Look for supplements where vitamin D is in the form of cholecalciferol, or vitamin D3.

The case for eating breakfast everyday is mounting. We already know that people who eat breakfast are generally thinner than those who do not. They also tend to eat a healthier diet overall. Now new data suggest that the nutritional quality of your breakfast is also important for your health. Surprise!

A study published in the latest issue of the American Journal of Clinical Nutrition is the first to address how your choice of breakfast is correlated with the quality of food chosen during the rest of the day. The scientists combined dietary data from three continuous National Health and Nutrition Examination Surveys (1999-2004) to determine energy density, nutritional quality and variety of foods eaten. They also examined the relationship between breakfast choices and body mass index (BMI). A total of 12,316 people were analyzed.

Eighty percent of people in the study reported eating breakfast. Although breakfast eaters ate more total daily calories during the study, the foods they chose tended to be of lower energy density. Lower energy density foods have fewer calories per gram and are usually associated with more nutritious fare such as fruits, vegetables and grains. Examples of higher energy density foods are meats, cheeses and processed carbohydrates.

Interestingly, breakfasts of lower energy density, such as cereal with milk and fruit, were an indication of a more diverse diet throughout the rest of the day. In other words, participants who ate cereal for breakfast were more likely to report eating a lot of fruits, vegetables, grains, legumes and other healthful foods overall. This was true whether or not breakfast itself was included in the calculation.

People who chose breakfasts of higher energy density ate fewer different kinds of foods, but more pastries and junk foods. Countless studies have shown that dietary diversity is one of the best predictors of good health. This was confirmed in this study, as higher energy density breakfasts predicted fewer beneficial micronutrients consumed overall.

The researchers also found that seventeen percent of people who ate breakfast reported items that could not be “grouped into the major food groups,” things such as pastries, confections and meal replacement drinks and bars. With this the authors of the study point out that a significant percentage of Americans do not eat “real food” for breakfast (somewhere Michael Pollan is smiling and nodding). Not surprisingly, this group comprised the highest average energy density of any type of breakfast.

Women (but not men) that did not eat breakfast had a higher average BMI. This was true regardless of body image or attempted weight loss. In both men and women, breakfast energy density showed a linear positive association with BMI. This means that even for people who do eat breakfast, if you eat foods with higher energy density you will probably weigh more.

In English, what this all means is that although eating breakfast alone does a body good, it is much better if your breakfast is cereal and fruit rather than eggs and meat.

There is no clear cause and effect in an analysis of this kind, however there seems to be a correlation between eating less healthy foods at breakfast and making poor food choices throughout the day. While it is possible that some people simply make unhealthy selections all the time, there is also a possibility that your breakfast choices affect metabolic and hormonal systems that alter your cravings for different foods over the course of the day. Indeed, there are studies showing that people who eat whole grains in the morning have altered insulin responses for nine to twelve hours after eating.

Even if your breakfast choice does not have a direct impact on the rest of your food selections, choosing cereals and fruit will certainly bring you a step closer to better health. Pouring a bowl of whole grain cereal and adding some fruit is pretty simple, and I guarantee you it is easier than making eggs and sausage. Do yourself a favor and save the cakes and donuts for dessert.

This article can also be found at Synapse.