Quick summary:
Poor iodine and selenium status in this German population, lower iodine and selenium status in vegetarians, and even lower in vegans.[My conclusion:
The Vegan Society’s supplement Veg1 is a helpful supplement for vegans in Germany.
Veg1 contains:
Vitamin D2: 10 mcg
Vitamin B2: 1.6 mg
Vitamin B6: 2 mg
Vitamin B12 (cyanocobalamin): 10 mcg
Folic acid: 200 mcg
Iodine: 150 mcg
Selenium: 60 mcg]
A doctoral thesis (MD) from southern Germany from January 2015 is centred around a study comparing iodine, selenium, zinc, and iron status in vegans, vegetarians, and omnivores.
As far as I’m aware these results haven’t been published in a journal, and haven’t been published in English at all. (The doctoral thesis, including the summary, is available in German only).
Because the results seem relevant for the field of vegan nutrition I have translated the most relevant findings into English.
1. Study
- Cross-sectional study
- Results published as a dissertation (doctoral thesis, Medical Doctor) at Ludwig-Maximilians-Universität (LMU) Munich, Germany
- Dissertation title (translation): “Significance of the iodine/selenium quotient and of ferritin for the occurrence of autoimmune thyroiditis (AIT) in subjects following an omnivorous, vegetarian or vegan diet”
- “Vegetarian” was defined as “no meat, poultry or fish”, i.e. ovo-lacto-vegetarian – so the vegetarian group did NOT include pescatarians or semi-vegetarians
1.1. Study period
May–December 2009 (southern Germany)1.2. Study participants
- Total n = 283
- Age range: 14–65 y
- At least 6 months on their respective diets
- No known history of thyroid disease
- No other chronic diseases
- Percentage of study participants who did not supplement iodine or selenium (neither of the two): 82% (68/83) of vegans
91% (92/101) of vegetarians
93% (92/99) omnivores
TABLE 1: Study particpiants
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diet group
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omnivore
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vegetarian
|
vegan
|
number
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99
|
101
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83
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number (women)
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n = 70 (71%)
|
n = 72 (71%)
|
n = 56 (67%)
|
number (men)
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n = 29 (29%)
|
n = 29 (29%)
|
n = 27 (33%)
|
age (mean ± SD)
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43.6 ± 12.5 y
|
39.1 ± 13.9 y
|
38.9 ± 13.1 y
|
age (median)
|
45 y
|
40 y
|
38 y
|
age (range)
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16–65 y
|
14–63 y
|
15–65 y
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2. Results
2.1. Summary of results:
- No clear correlation between iodine/selenium quotient and AIT (autoimmune thyroiditis)
- Clear correlation between ferritin deficiency and AIT
- Still high prevalence of iodine deficiency in Germany (despite iodine prophylaxis)
- Poor selenium status in Germany
- Vegetarians and especially vegans have worse iodine and selenium status
- Incidence of AIT is higher in vegetarians, and especially vegans
- Sonography test results typical of AIT more common in vegetarians and vegans
- All three diet groups (omnivores, vegetarians, vegans) were within the reference range for zinc, but lower status in vegetarians, and yet lower in vegans
2.2. Table 2
TABLE
2: Concentrations of trace elements in the three diet groups
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SePP
(mg/L)
|
Selenium
(μg/L)a
|
Iodine
in urine (μg/L)
|
Ferritin
(μg/L)
|
Zinc
(μg/L)
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||
Reference ranges
|
±
3 mg/L
|
70–140
μg/L
|
100–200
μg/L
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30–300 μg/L
|
650–1200 μg/L
|
|
Omnivores
(n = 99)
|
mean
|
2.78
|
84.72
|
67.1
|
94.9
|
1141.71
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SD
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± 0.55
|
± 21.18
|
± 50.9
|
± 93.7
|
± 1037.56
|
|
median
|
2.68
|
83.2
|
50.7
|
65
|
988.1
|
|
range
|
1.51–4.17
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49.6–189.4
|
3.47–252.97
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5–586
|
403.3–2190.2
|
|
Vegetarians
(n = 101)
|
mean
|
2.6
|
69.4
|
55.7
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38.63
|
961.65
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SD
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± 0.6
|
± 16.48
|
± 56.03
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± 30.5
|
± 248.66
|
|
median
|
2.56
|
68.9
|
33.01
|
29
|
920
|
|
range
|
1.53–4.32
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36.9–114.5
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2.06–305.5
|
5–154
|
412.8–2353.1
|
|
Vegans
(n = 83)
|
mean
|
2.26
|
59.43
|
24.4
|
46.65
|
883.29
|
SD
|
± 0.52
|
± 19.02
|
± 33.09
|
± 41.1
|
± 186.77
|
|
median
|
2.24
|
56.7
|
13.15
|
39
|
865.7
|
|
range
|
1.16–3.92
|
21.7–125.7
|
0.28–168.64
|
10–318
|
581.5–1519.2
|
|
a Note that the author gives a
different reference range for plasma selenium on page 33/32: 50–120 μg/L. The vegan participants’ mean and median values are
within this range. But the author writes that more and more experts recommend
the lower value for plasma selenium to be at least 80–95 μg/L.
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SD: Standard
deviation
SePP: Selenoprotein P
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||||||
2.3. Further results
Selenium:
- Selenium status: vegetarians and vegans deficient, omnivores in low reference range
- Insufficient selenium status (<3 mg/L SePP): -- 91.6% of vegans
- GPx activity was normal in all three diet groups.
-- 74.3% of vegetarians
-- 67.7% of omnivores
Iodine:
- Iodine status: all groups deficient, vegans had most evident deficiency
- 66.3% of vegans had severe iodine deficiency (iodinuria <20 μg/L); 6% of vegans had optimal iodine status (iodinuria 100 – 199 μg/L)
- Sonography test results of thyroid typical of AIT (autoimmune thyroiditis): 14% (n = 12) of vegans; 11% (n = 11) of vegetarians; 10% (n = 10) of omnivores
- Mean TSH was normal in all three diet groups.
- Mean TSH levels: 1.92 μg/mL in vegans; 1.64 μg/mL in vegetarians; 1.52 μg/mL in omnivores [see TABLE 23 “Tab. 23” in the thesis]
Iron:
- Plasma iron was normal in all three groups
- Ferritin <30 μg/L: 36% of vegans; 51% of vegetarians; 21% of omnivores
Zinc:
- [Plasma] zinc: all groups within the reference range, but vegetarians lower than omnivores, and vegans lower than vegetarians
3. Additional information
- The author concluded that if selenium, iodine and ferritin levels are too low the risk for AIT is increased.
- 25% of women and 10% of men in Germany seem to have a goiter.
- In Crohn’s disease, rheumatoid arthritis, and asthma, plasma selenium levels and GPx activity correlate inversely with severity of symptoms.
- The thyroid gland contains large amounts of selenium.
- Reference range for TSH at LMU Munich and in this study: 0.3–4.0 µIU/mL
- Recommended daily intake of iodine (according to the author) for adequate thyroid function: 150–250 µg
- 100 µg/day prevent iodine deficiency symptoms.
- According to the WHO iodine intake in Germany – due to consistent iodine prophylaxis [iodized salt] – is high enough so that iodine deficiency associated mental retardation hardly [!] occurs.
- The food industry and large-scale caterers (canteens etc.) in Germany are supposed to use iodized salt by law [I’m not sure how widely this is done and to what extent it is obligatory]. Because of this iodine intake in the general population in Germany is almost adequate. There generally seems to be no risk of iodine excess in Germany.
- DGE (German Society for Nutrition) recommendations for iodine intake: adults <50 y: 200 mcg/d; adults >50 y 180 mcg/d. The typical German diet does NOT provide these amounts.
- DGE food recommendations to improve iodine status: 1–2 portions of sea fish (150 g each) per week. However à example: if consumed as salmon: 300–600 µg iodine per week ß still clearly below the weekly recommendation of 1,400 µg.
- The selenium content in plants depends on the selenium content in the soil [other factors apply].
- Author: Up to 50% of selenium intake can potentially come from plant foods.
- The author names "dates and mushrooms" as potential plant sources of zinc (other than legumes, whole grains and nuts/seeds). [Dates however seem to contain little selenium, and I'm not sure about the bioavailability of selenium from mushrooms. If the bioavailability is high, they might be good sources of selenium.]
- When selecting participants the researchers looked for people who did not supplement their diets with selenium or iodine.
- Recruiting vegans was more difficult than expected.
- Since 1979, 15 studies have determined plasma selenium levels in Germany with means between 63 μg/L and 94 μg/L
- Selenium intakes in Austria: 37–68 µg/d [Typical selenium intakes in Germany aren’t given.]
- To maximize SePP plasma concentrations a selenium intake of more than 90 μg/d seems to be necessary.
4. Quotes from the dissertation
- “A further factor that surely applies to all three diet groups, is that one can eat an unbalanced or balanced diet in each of the diet groups – which is something that also became apparent during the course of this study.”
- GERMAN: „Ein weiterer Faktor, der sicher für alle drei Ernährungsgruppen zutrifft, ist, dass man sich in jeder Ernährungsgruppe einseitig oder ausgewogen ernähren kann, was im Rahmen der Studie auch deutlich wurde.”
- “For this reason further intensive strategies with the aim to ensure an additional supply of iodine and selenium for the population should be discussed.”
- GERMAN: „Aus diesem Grund sollten weiterhin intensive Strategien zur zusätzlichen Versorgung der Bevölkerung mit Jod und Selen diskutiert werden.”
- “The importance of a balanced diet and the necessity of fortification with iodine and selenium should therefore reach the awareness of the public to a greater extent, in order to avert long-term negative health outcomes.”
- GERMAN: „Die Wichtigkeit einer ausgewogenen Ernährung und die Notwendigkeit der Anreicherung von Jod und Selen sollte daher noch mehr ins Bewusstsein der Bevölkerung vordringen, um langfristige Schäden abzuwenden.”
- “The evidence presented here should reinforce the efforts to further improve iodine intakes in Germany and to think about potential solutions regarding the progressive selenium deficiency in Germany.”
- GERMAN: „Die hier erbachten Nachweise sollten die Bemühungen bestärken, die Jodversorgung in Deutschland weiter voranzutreiben und über Lösungsansätze bezüglich des progredienten Selenmangels in Deutschland nachzudenken.”