Consuming eggs to maintain vitamin D status

Eating eggs can attenuate the decline in wintertime vitamin D status but how many eggs are needed to see a meaningful effect?

First, the vitamin D content of eggs

Eggs are one of the few natural sources rich in vitamin D containing both vitamin D3 and 25-hydroxyvitamin D [25(OH)D3] - the latter being up to five times the relative biological activity of vitamin D.

This means that the 25(OH)D level in an egg is five times more potent at increasing 25(OH)D levels - the major form of vitamin D circulating in blood.

Vitamin D content of eggs will vary based on geographical location, feed fortification and animal production practices. Both vitamin D and 25(OH)D is used as a fortificant in animal feed.



On average, the vitamin D content per egg (60 g):

• Vitamin D3 ranges from 0.4 to 0.8 micrograms;
• 25(OH)D3 ranges from 0.4 to 0.6 micrograms

Given the high potency of 25(OH)D3 content, a correction factor of 5 times can be applied resulting in a total vitamin D activity per egg:

• 2.5 to 3.4 micrograms or 100 to 135 IU

Interestingly, 25(OH)D3 is not recognized in the Australia NZ Food Standards Code as contributing to the vitamin D content of foods. Most food composition tables report vitamin D content of foods as the sum of vitamin D3 and vitamin D2 only.

Next, what is the recommended dietary intake of vitamin D for healthy adults?

Most countries recommend a daily intake ranging from of 5 to 15 μg/day (200-600 IU/day).

• NZ and Australia: Adequate intake (AI) of vitamin D for individuals aged 1–50 years is 5 μg/day (200 IU/d), increasing to 10 μg/day (400 IU/d) for 51–70 year olds, and 15 μg/day (600 IU/d) for those aged >70 years.
• US and Canada: Recommended Dietary Allowance (RDA) of 15 μg/day (600 IU/d) for those aged 1 to >70 years.

And finally, the research study

A randomised controlled study published last month in Journal of Nutrition evaluated the dose-response effect of consuming 2, 7 or 12 eggs per week on serum 25(OH)D concentrations over 12 weeks during the autumn-winter months
 
In addition to vitamin D status as the primary outcome, they also investigated changes in serum lipids along with the feasibility and acceptability of consuming eggs over this period.

The researchers tested the eggs consumed in the study finding a total vitamin D activity level: 5.2 μg per egg.

Sun exposure and protection practices (usual time spent outdoors between 10 am - 2 pm) were collected.
 
Egg acceptability measurements including whether they liked eating the eggs, whether they liked the taste of eggs, how satisfied they felt after eating the eggs, how easy/difficult it was for them to prepare the eggs to eat, the level of effort required to eat the eggs, whether eating out influenced regular egg consumption, and the ease at which they could continue to eat the same number of prescribed eggs after completion of the study.

Study compliance was fairly good at 84% compliance, and adherence did not differ between treatment groups.
 
Changes in 25(OH)D concentrations

Controls: Participants consuming only 2 eggs per week experienced a serum 25(OH)D reduction of 29 nmol/L over the 12-week study period.

Treatment: Participants assigned to the 7 and 12 eggs per week experienced a slightly non-significant reduction 7-8 nmol/L.
 
Were cholesterol levels through the roof?

No. Although not powered to detect differences in blood cholesterol concentrations, there was no statistically significant differences in cholesterol between the different egg groups.

The 12-egg per week intervention provided around an extra 400 mg/d cholesterol, which lead to significant within group increases in total (0.47 mmol/L) and LDL-C (0.41 mmol/L). This small observed increase in blood cholesterol is in line with the modelling discussed last week in Issue 33.

The average amount of saturated fat in the background diet was around 13% of total energy (TE) – higher than the recommended levels of less than 10% TE.

A reduction in saturated fat to recommended levels is likely to have a cholesterol-lowering effect that outweighs any hypercholesterolaemic effects of eggs.

Acceptability - too many eggs?

Overall, participants rated highly that they liked eating the eggs and their taste, and that it was not too difficult or too much effort to consume their prescribed dose of eggs.

Bottom Line

Winter eggs for the win!

Collectively, these findings indicate that consumption of 7 commercially available eggs per week, which is in line with most dietary guidelines, represents a safe and effective dietary approach to attenuate the wintertime decrease in circulating 25(OH)D concentrations in healthy adults residing in southern Australia (or likely a similar latitude).